[gnu-emacs] / doc / emacs / glossary.texi

@c This is part of the Emacs manual.
@c Copyright (C) 1985-1987, 1993-1995, 1997, 2001-2015 Free Software
@c Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Glossary
@unnumbered Glossary
@cindex glossary

@table @asis
@anchor{Glossary---Abbrev}
@item Abbrev
An abbrev is a text string that expands into a different text string
when present in the buffer.  For example, you might define a few letters
as an abbrev for a long phrase that you want to insert frequently.
@xref{Abbrevs}.

@item Aborting
Aborting means getting out of a recursive edit (q.v.).  The
commands @kbd{C-]} and @kbd{M-x top-level} are used for this.
@xref{Quitting}.

@item Active Region
Setting the mark (q.v.@:) at a position in the text also activates it.
When the mark is active, we call the region an active region.
@xref{Mark}.

@item Alt
Alt is the name of a modifier bit that a keyboard input character may
have.  To make a character Alt, type it while holding down the @key{Alt}
key.  Such characters are given names that start with @kbd{@key{Alt}-}
(usually written @kbd{A-} for short).  (Note that many terminals have a
key labeled @key{Alt} that is really a @key{META} key.)  @xref{User
Input, Alt}.

@item Argument
@xref{Glossary---Numeric Argument}.

@item @acronym{ASCII} character
An @acronym{ASCII} character is either an @acronym{ASCII} control
character or an @acronym{ASCII} printing character.  @xref{User Input}.

@item @acronym{ASCII} control character
An @acronym{ASCII} control character is the Control version of an upper-case
letter, or the Control version of one of the characters @samp{@@[\]^_?}.

@item @acronym{ASCII} printing character
@acronym{ASCII} letters, digits, space, and the following punctuation
characters: @samp{!@@#$%^&*()_-+=|\~`@{@}[]:;"'<>,.?/}.

@item Auto Fill Mode
Auto Fill mode is a minor mode (q.v.@:) in which text that you insert is
automatically broken into lines of a given maximum width.
@xref{Filling}.

@item Auto Saving
Auto saving is the practice of periodically saving the contents of an
Emacs buffer in a specially-named file, so that the information will
be preserved if the buffer is lost due to a system error or user error.
@xref{Auto Save}.

@item Autoloading
Emacs can automatically load Lisp libraries when a Lisp program requests a
function from those libraries.  This is called ``autoloading''.
@xref{Lisp Libraries}.

@item Backtrace
A backtrace is a trace of a series of function calls showing how a
program arrived at a certain point.  It is used mainly for finding and
correcting bugs (q.v.).  Emacs can display a backtrace when it signals
an error or when you type @kbd{C-g} (@pxref{Glossary---Quitting}).
@xref{Checklist}.

@item Backup File
A backup file records the contents that a file had before the current
editing session.  Emacs makes backup files automatically to help you
track down or cancel changes you later regret making.  @xref{Backup}.

@item Balancing Parentheses
Emacs can balance parentheses (or other matching delimiters) either
manually or automatically.  You do manual balancing with the commands
to move over parenthetical groupings (@pxref{Moving by Parens}).
Automatic balancing works by blinking or highlighting the delimiter
that matches the one you just inserted, or inserting the matching
delimiter for you (@pxref{Matching,,Matching Parens}).

@anchor{Glossary---Balanced Expression}
@item Balanced Expressions
A balanced expression is a syntactically recognizable expression, such
as a symbol, number, string constant, block, or parenthesized expression
in C@.  @xref{Expressions,Balanced Expressions}.

@item Balloon Help
@xref{Glossary---Tooltips}.

@item Base Buffer
A base buffer is a buffer whose text is shared by an indirect buffer
(q.v.).

@item Bidirectional Text
Some human languages, such as English, are written from left to right.
Others, such as Arabic, are written from right to left.  Emacs
supports both of these forms, as well as any mixture of them---this
is ``bidirectional text''.  @xref{Bidirectional Editing}.

@item Bind
To bind a key sequence means to give it a binding (q.v.).
@xref{Rebinding}.

@anchor{Glossary---Binding}
@item Binding
A key sequence gets its meaning in Emacs by having a binding, which is a
command (q.v.), a Lisp function that is run when you type that
sequence.  @xref{Commands,Binding}.  Customization often involves
rebinding a character to a different command function.  The bindings of
all key sequences are recorded in the keymaps (q.v.).  @xref{Keymaps}.

@item Blank Lines
Blank lines are lines that contain only whitespace.  Emacs has several
commands for operating on the blank lines in the buffer.  @xref{Blank Lines}.

@item Bookmark
Bookmarks are akin to registers (q.v.@:) in that they record positions
in buffers to which you can return later.  Unlike registers, bookmarks
persist between Emacs sessions.  @xref{Bookmarks}.

@item Border
A border is a thin space along the edge of the frame, used just for
spacing, not for displaying anything.  An Emacs frame has an ordinary
external border, outside of everything including the menu bar, plus an
internal border that surrounds the text windows, their scroll bars
and fringes, and separates them from the menu bar and tool bar.  You
can customize both borders with options and resources (@pxref{Borders
X}).  Borders are not the same as fringes (q.v.).

@item Buffer
The buffer is the basic editing unit; one buffer corresponds to one text
being edited.  You normally have several buffers, but at any time you are
editing only one, the current buffer, though several can be visible
when you are using multiple windows or frames (q.v.).  Most buffers
are visiting (q.v.@:) some file.  @xref{Buffers}.

@item Buffer Selection History
Emacs keeps a buffer selection history that records how recently each
Emacs buffer has been selected.  This is used for choosing a buffer to
select.  @xref{Buffers}.

@item Bug
A bug is an incorrect or unreasonable behavior of a program, or
inaccurate or confusing documentation.  Emacs developers treat bug
reports, both in Emacs code and its documentation, very seriously and
ask you to report any bugs you find.  @xref{Bugs}.

@item Button Down Event
A button down event is the kind of input event (q.v.@:) generated
right away when you press down on a mouse button.  @xref{Mouse Buttons}.

@item By Default
@xref{Glossary---Default}.

@item Byte Compilation
@xref{Glossary---Compilation}.

@anchor{Glossary---C-}
@item @kbd{C-}
@kbd{C-} in the name of a character is an abbreviation for Control.
@xref{User Input,C-}.

@item @kbd{C-M-}
@kbd{C-M-} in the name of a character is an abbreviation for
Control-Meta.  If your terminal lacks a real @key{META} key, you type
a Control-Meta character by typing @key{ESC} and then typing the
corresponding Control character.  @xref{User Input,C-M-}.

@item Case Conversion
Case conversion means changing text from upper case to lower case or
vice versa.  @xref{Case}.

@item Case Folding
Case folding means ignoring the differences between case variants of
the same letter: upper-case, lower-case, and title-case.  Emacs
performs case folding by default in text search.  @xref{Lax Search}.

@item Character
Characters form the contents of an Emacs buffer.  Also, key sequences
(q.v.@:) are usually made up of characters (though they may include
other input events as well).  @xref{User Input}.

@item Character Folding
Character folding means ignoring differences between similarly looking
characters, such as between @code{a}, and @code{@:a} and @code{@'a}.
Emacs performs character folding by default in text search.  @xref{Lax
Search}.

@item Character Set
Emacs supports a number of character sets, each of which represents a
particular alphabet or script.  @xref{International}.

@item Character Terminal
@xref{Glossary---Text Terminal}.

@item Click Event
A click event is the kind of input event (q.v.@:) generated when you
press a mouse button and release it without moving the mouse.
@xref{Mouse Buttons}.

@item Client
@xref{Glossary---Server}.

@item Clipboard
A clipboard is a buffer provided by the window system for transferring
text between applications.  On the X Window System, the clipboard is
provided in addition to the primary selection (q.v.); on MS-Windows and Mac,
the clipboard is used @emph{instead} of the primary selection.
@xref{Clipboard}.

@item Coding System
A coding system is an encoding for representing text characters in a
file or in a stream of information.  Emacs has the ability to convert
text to or from a variety of coding systems when reading or writing it.
@xref{Coding Systems}.

@item Command
A command is a Lisp function specially defined to be able to serve as a
key binding in Emacs.  When you type a key sequence (q.v.), its
binding (q.v.@:) is looked up in the relevant keymaps (q.v.@:) to find
the command to run.  @xref{Commands}.

@item Command History
@xref{Glossary---Minibuffer History}.

@item Command Name
A command name is the name of a Lisp symbol that is a command
(@pxref{Commands}).  You can invoke any command by its name using
@kbd{M-x} (@pxref{M-x,M-x,Running Commands by Name}).

@item Comment
A comment is text in a program which is intended only for humans reading
the program, and which is specially marked so that it will be ignored
when the program is loaded or compiled.  Emacs offers special commands
for creating, aligning and killing comments.  @xref{Comments}.

@item Common Lisp
Common Lisp is a dialect of Lisp (q.v.@:) much larger and more powerful
than Emacs Lisp.  Emacs provides a subset of Common Lisp in the CL
package.  @xref{Top, Common Lisp, Overview, cl, Common Lisp Extensions}.

@anchor{Glossary---Compilation}
@item Compilation
Compilation is the process of creating an executable program from source
code.  Emacs has commands for compiling files of Emacs Lisp code
(@pxref{Byte Compilation,,, elisp, the Emacs Lisp
Reference Manual}) and programs in C and other languages
(@pxref{Compilation}).

@item Complete Key
A complete key is a key sequence that fully specifies one action to be
performed by Emacs.  For example, @kbd{X} and @kbd{C-f} and @kbd{C-x m}
are complete keys.  Complete keys derive their meanings from being bound
(q.v.@:) to commands (q.v.).  Thus, @kbd{X} is conventionally bound to
a command to insert @samp{X} in the buffer; @kbd{C-x m} is
conventionally bound to a command to begin composing a mail message.
@xref{Keys}.

@item Completion
Completion is what Emacs does when it automatically expands an
abbreviation for a name into the entire name.  Completion is done for
minibuffer (q.v.@:) arguments when the set of possible valid inputs
is known; for example, on command names, buffer names, and
file names.  Completion usually occurs when @key{TAB}, @key{SPC} or
@key{RET} is typed.  @xref{Completion}.

@anchor{Glossary---Continuation Line}
@item Continuation Line
When a line of text is longer than the width of the window, it
normally (but see @ref{Glossary---Truncation}) takes up more than one
screen line when displayed.  We say that the text line is continued, and all
screen lines used for it after the first are called continuation
lines.  @xref{Continuation Lines}.  A related Emacs feature is
filling (q.v.).

@item Control Character
A control character is a character that you type by holding down the
@key{Ctrl} key.  Some control characters also have their own keys, so
that you can type them without using @key{Ctrl}.  For example,
@key{RET}, @key{TAB}, @key{ESC} and @key{DEL} are all control
characters.  @xref{User Input}.

@item Copyleft
A copyleft is a notice giving the public legal permission to
redistribute and modify a program or other work of art, but requiring
modified versions to carry similar permission.  Copyright is normally
used to keep users divided and helpless; with copyleft we turn that
around to empower users and encourage them to cooperate.

The particular form of copyleft used by the GNU project is called the
GNU General Public License.  @xref{Copying}.

@item @key{Ctrl}
The @key{Ctrl} or control key is what you hold down
in order to enter a control character (q.v.).  @xref{Glossary---C-}.

@item Current Buffer
The current buffer in Emacs is the Emacs buffer on which most editing
commands operate.  You can select any Emacs buffer as the current one.
@xref{Buffers}.

@item Current Line
The current line is the line that point is on (@pxref{Point}).

@item Current Paragraph
The current paragraph is the paragraph that point is in.  If point is
between two paragraphs, the current paragraph is the one that follows
point.  @xref{Paragraphs}.

@item Current Defun
The current defun is the defun (q.v.@:) that point is in.  If point is
between defuns, the current defun is the one that follows point.
@xref{Defuns}.

@item Cursor
The cursor is the rectangle on the screen which indicates the position
(called point; q.v.@:) at which insertion and deletion takes place.
The cursor is on or under the character that follows point.  Often
people speak of ``the cursor'' when, strictly speaking, they mean
``point''.  @xref{Point,Cursor}.

@item Customization
Customization is making minor changes in the way Emacs works, to
reflect your preferences or needs.  It is often done by setting
variables (@pxref{Variables}) or faces (@pxref{Face Customization}),
or by rebinding key sequences (@pxref{Keymaps}).

@cindex cut and paste
@item Cut and Paste
@xref{Glossary---Killing}, and @ref{Glossary---Yanking}.

@anchor{Glossary---Daemon}
@item Daemon
A daemon is a standard term for a system-level process that runs in the
background.  Daemons are often started when the system first starts up.
When Emacs runs in daemon-mode, it runs in the background and does not
open a display.  You can then connect to it with the
@command{emacsclient} program.  @xref{Emacs Server}.

@item Default Argument
The default for an argument is the value that will be assumed if you
do not specify one.  When the minibuffer is used to read an argument,
the default argument is used if you just type @key{RET}.
@xref{Minibuffer}.

@anchor{Glossary---Default}
@item Default
A default is the value that is used for a certain purpose when
you do not explicitly specify a value to use.

@item Default Directory
When you specify a file name that does not start with @samp{/} or @samp{~},
it is interpreted relative to the current buffer's default directory.
(On MS systems, file names that start with a drive letter
@samp{@var{x}:} are treated as absolute, not relative.)
@xref{Minibuffer File,Default Directory}.

@item Defun
A defun is a major definition at the top level in a program.  The name
``defun'' comes from Lisp, where most such definitions use the construct
@code{defun}.  @xref{Defuns}.

@item @key{DEL}
@key{DEL} is a character that runs the command to delete one character
of text before the cursor.  It is typically either the @key{Delete}
key or the @key{BACKSPACE} key, whichever one is easy to type.
@xref{Erasing,DEL}.

@item Deletion
Deletion means erasing text without copying it into the kill ring
(q.v.).  The alternative is killing (q.v.).  @xref{Killing,Deletion}.

@anchor{Glossary---Deletion of Files}
@item Deletion of Files
Deleting a file means erasing it from the file system.
(Note that some systems use the concept of a trash can, or recycle
bin, to allow you to undelete files.)
@xref{Misc File Ops,Misc File Ops,Miscellaneous File Operations}.

@item Deletion of Messages
Deleting a message (in Rmail, and other mail clients) means flagging
it to be eliminated from your mail file.  Until you expunge (q.v.@:)
the Rmail file, you can still undelete the messages you have deleted.
@xref{Rmail Deletion}.

@item Deletion of Windows
Deleting a window means eliminating it from the screen.  Other windows
expand to use up the space.  The text that was in the window is not
lost, and you can create a new window with the same dimensions as the
old if you wish.  @xref{Windows}.

@item Directory
File directories are named collections in the file system, within which
you can place individual files or subdirectories.  They are sometimes
referred to as ``folders''.  @xref{Directories}.

@anchor{Glossary---Directory Local Variable}
@item Directory Local Variable
A directory local variable is a local variable (q.v.@:) that applies
to all the files within a certain directory.  @xref{Directory
Variables}.

@item Dired
Dired is the Emacs facility that displays the contents of a file
directory and allows you to ``edit the directory'', performing
operations on the files in the directory.  @xref{Dired}.

@item Disabled Command
A disabled command is one that you may not run without special
confirmation.  The usual reason for disabling a command is that it is
confusing for beginning users.  @xref{Disabling}.

@item Down Event
Short for ``button down event'' (q.v.).

@item Drag Event
A drag event is the kind of input event (q.v.@:) generated when you
press a mouse button, move the mouse, and then release the button.
@xref{Mouse Buttons}.

@item Dribble File
A dribble file is a file into which Emacs writes all the characters that
you type on the keyboard.  Dribble files can be used to make a record
for debugging Emacs bugs.  Emacs does not make a dribble file unless you
tell it to.  @xref{Bugs}.

@c TODO?  Not really appropriate for the user manual I think.
@c Dynamic Binding

@item Echo Area
The echo area is the bottom line of the screen, used for echoing the
arguments to commands, for asking questions, and showing brief messages
(including error messages).  The messages are stored in the buffer
@file{*Messages*} so you can review them later.  @xref{Echo Area}.

@item Echoing
Echoing is acknowledging the receipt of input events by displaying
them (in the echo area).  Emacs never echoes single-character key
sequences; longer key sequences echo only if you pause while typing
them.

@item Electric
We say that a character is electric if it is normally self-inserting
(q.v.), but the current major mode (q.v.@:) redefines it to do something
else as well.  For example, some programming language major modes define
particular delimiter characters to reindent the line, or insert one or
more newlines in addition to self-insertion.

@anchor{Glossary---End Of Line}
@item End Of Line
End of line is a character or a sequence of characters that indicate
the end of a text line.  On GNU and Unix systems, this is a newline
(q.v.), but other systems have other conventions.  @xref{Coding
Systems,end-of-line}.  Emacs can recognize several end-of-line
conventions in files and convert between them.

@item Environment Variable
An environment variable is one of a collection of variables stored by
the operating system, each one having a name and a value.  Emacs can
access environment variables set by its parent shell, and it can set
variables in the environment it passes to programs it invokes.
@xref{Environment}.

@item EOL
@xref{Glossary---End Of Line}.

@item Error
An error occurs when an Emacs command cannot execute in the current
circumstances.  When an error occurs, execution of the command stops
(unless the command has been programmed to do otherwise) and Emacs
reports the error by displaying an error message (q.v.).
@c Not helpful?
@c Type-ahead is discarded.  Then Emacs is ready to read another
@c editing command.

@item Error Message
An error message is output displayed by Emacs when you ask it to do
something impossible (such as, killing text forward when point is at
the end of the buffer), or when a command malfunctions in some way.
Such messages appear in the echo area, accompanied by a beep.

@item @key{ESC}
@key{ESC} is a character used as a prefix for typing Meta characters on
keyboards lacking a @key{META} key.  Unlike the @key{META} key (which,
like the @key{SHIFT} key, is held down while another character is
typed), you press the @key{ESC} key as you would press a letter key, and
it applies to the next character you type.

@item Expression
@xref{Glossary---Balanced Expression}.

@item Expunging
Expunging an Rmail, Gnus newsgroup, or Dired buffer is an operation
that truly discards the messages or files you have previously flagged
for deletion.

@item Face
A face is a style of displaying characters.  It specifies attributes
such as font family and size, foreground and background colors,
underline and strike-through, background stipple, etc.  Emacs provides
features to associate specific faces with portions of buffer text, in
order to display that text as specified by the face attributes.
@xref{Faces}.

@item File Local Variable
A file local variable is a local variable (q.v.@:) specified in a
given file.  @xref{File Variables}, and @ref{Glossary---Directory
Local Variable}.

@anchor{Glossary---File Locking}
@item File Locking
Emacs uses file locking to notice when two different users
start to edit one file at the same time.  @xref{Interlocking}.

@item File Name
@c This is fairly tautological...
A file name is a name that refers to a file.  File names may be relative
or absolute; the meaning of a relative file name depends on the current
directory, but an absolute file name refers to the same file regardless
of which directory is current.  On GNU and Unix systems, an absolute
file name starts with a slash (the root directory) or with @samp{~/} or
@samp{~@var{user}/} (a home directory).  On MS-Windows/MS-DOS, an
absolute file name can also start with a drive letter and a colon, e.g.,
@samp{@var{d}:}.

Some people use the term ``pathname'' for file names, but we do not;
we use the word ``path'' only in the term ``search path'' (q.v.).

@item File-Name Component
A file-name component names a file directly within a particular
directory.  On GNU and Unix systems, a file name is a sequence of
file-name components, separated by slashes.  For example, @file{foo/bar}
is a file name containing two components, @samp{foo} and @samp{bar}; it
refers to the file named @samp{bar} in the directory named @samp{foo} in
the current directory.  MS-DOS/MS-Windows file names can also use
backslashes to separate components, as in @file{foo\bar}.

@item Fill Prefix
The fill prefix is a string that should be expected at the beginning
of each line when filling is done.  It is not regarded as part of the
text to be filled.  @xref{Filling}.

@anchor{Glossary---Filling}
@item Filling
Filling text means adjusting the position of line-breaks to shift text
between consecutive lines, so that all the lines are approximately the
same length.  @xref{Filling}.  Some other editors call this feature
``line wrapping''.

@anchor{Glossary---Font Lock}
@item Font Lock
Font Lock is a mode that highlights parts of buffer text in different
faces, according to the syntax.  Some other editors refer to this as
``syntax highlighting''.  For example, all comments (q.v.@:)
might be colored red.  @xref{Font Lock}.

@item Fontset
A fontset is a named collection of fonts.  A fontset specification lists
character sets and which font to use to display each of them.  Fontsets
make it easy to change several fonts at once by specifying the name of a
fontset, rather than changing each font separately.  @xref{Fontsets}.

@item Formfeed Character
@xref{Glossary---Page}.

@item Frame
A frame is a rectangular cluster of Emacs windows.  Emacs starts out
with one frame, but you can create more.  You can subdivide each frame
into Emacs windows (q.v.).  When you are using a window system
(q.v.), more than one frame can be visible at the same time.
@xref{Frames}.  Some other editors use the term ``window'' for this,
but in Emacs a window means something else.

@item Free Software
Free software is software that gives you the freedom to share, study
and modify it.  Emacs is free software, part of the GNU project
(q.v.), and distributed under a copyleft (q.v.@:) license called the
GNU General Public License.  @xref{Copying}.

@anchor{Glossary---Free Software Foundation}
@item Free Software Foundation
The Free Software Foundation (FSF) is a charitable foundation
dedicated to promoting the development of free software (q.v.).
For more information, see @uref{http://fsf.org/, the FSF website}.

@item Fringe
On a graphical display (q.v.), there's a narrow portion of the frame
(q.v.@:) between the text area and the window's border.  These
``fringes'' are used to display symbols that provide information about
the buffer text (@pxref{Fringes}).  Emacs displays the fringe using a
special face (q.v.@:) called @code{fringe}.  @xref{Faces,fringe}.

@item FSF
@xref{Glossary---Free Software Foundation}.

@item FTP
FTP is an acronym for File Transfer Protocol.  This is one standard
method for retrieving remote files (q.v.).

@item Function Key
A function key is a key on the keyboard that sends input but does not
correspond to any character.  @xref{Function Keys}.

@item Global
Global means ``independent of the current environment; in effect
throughout Emacs''.  It is the opposite of local (q.v.).  Particular
examples of the use of ``global'' appear below.

@item Global Abbrev
A global definition of an abbrev (q.v.@:) is effective in all major
modes that do not have local (q.v.@:) definitions for the same abbrev.
@xref{Abbrevs}.

@item Global Keymap
The global keymap (q.v.@:) contains key bindings that are in effect
everywhere, except when overridden by local key bindings in a major
mode's local keymap (q.v.).  @xref{Keymaps}.

@item Global Mark Ring
The global mark ring records the series of buffers you have recently
set a mark (q.v.@:) in.  In many cases you can use this to backtrack
through buffers you have been editing, or in which you have found
tags (@pxref{Glossary---Tags Table}).  @xref{Global Mark Ring}.

@anchor{Glossary---Global Substitution}
@item Global Substitution
Global substitution means replacing each occurrence of one string by
another string throughout a large amount of text.  @xref{Replace}.

@item Global Variable
The global value of a variable (q.v.@:) takes effect in all buffers
that do not have their own local (q.v.@:) values for the variable.
@xref{Variables}.

@item GNU
GNU is a recursive acronym for GNU's Not Unix, and it refers to a
Unix-compatible operating system which is free software (q.v.).
@xref{Manifesto}.  GNU is normally used with Linux as the kernel since
Linux works better than the GNU kernel.  For more information, see
@uref{http://www.gnu.org/, the GNU website}.

@item Graphic Character
Graphic characters are those assigned pictorial images rather than
just names.  All the non-Meta (q.v.@:) characters except for the
Control (q.v.@:) characters are graphic characters.  These include
letters, digits, punctuation, and spaces; they do not include
@key{RET} or @key{ESC}.  In Emacs, typing a graphic character inserts
that character (in ordinary editing modes).  @xref{Inserting Text}.

@item Graphical Display
A graphical display is one that can display images and multiple fonts.
Usually it also has a window system (q.v.).

@item Highlighting
Highlighting text means displaying it with a different foreground and/or
background color to make it stand out from the rest of the text in the
buffer.

Emacs uses highlighting in several ways.  It highlights the region
whenever it is active (@pxref{Mark}).  Incremental search also
highlights matches (@pxref{Incremental Search}).  @xref{Glossary---Font Lock}.

@item Hardcopy
Hardcopy means printed output.  Emacs has various commands for
printing the contents of Emacs buffers.  @xref{Printing}.

@item @key{HELP}
@key{HELP} is the Emacs name for @kbd{C-h} or @key{F1}.  You can type
@key{HELP} at any time to ask what options you have, or to ask what a
command does.  @xref{Help}.

@item Help Echo
Help echo is a short message displayed in the echo area (q.v.@:) when
the mouse pointer is located on portions of display that require some
explanations.  Emacs displays help echo for menu items, parts of the
mode line, tool-bar buttons, etc.  On graphical displays, the messages
can be displayed as tooltips (q.v.).  @xref{Tooltips}.

@item Home Directory
Your home directory contains your personal files.  On a multi-user GNU
or Unix system, each user has his or her own home directory.  When you
start a new login session, your home directory is the default
directory in which to start.  A standard shorthand for your home
directory is @samp{~}.  Similarly, @samp{~@var{user}} represents the
home directory of some other user.

@item Hook
A hook is a list of functions to be called on specific occasions, such
as saving a buffer in a file, major mode activation, etc.  By
customizing the various hooks, you can modify Emacs's behavior without
changing any of its code.  @xref{Hooks}.

@item Hyper
Hyper is the name of a modifier bit that a keyboard input character may
have.  To make a character Hyper, type it while holding down the
@key{Hyper} key.  Such characters are given names that start with
@kbd{Hyper-} (usually written @kbd{H-} for short).  @xref{User Input}.

@item Iff
``Iff'' means ``if and only if''.  This terminology comes from
mathematics.  Try to avoid using this term in documentation, since
many are unfamiliar with it and mistake it for a typo.

@item Inbox
An inbox is a file in which mail is delivered by the operating system.
Rmail transfers mail from inboxes to Rmail files in which the
mail is then stored permanently or until explicitly deleted.
@xref{Rmail Inbox}.

@anchor{Glossary---Incremental Search}
@item Incremental Search
Emacs provides an incremental search facility, whereby Emacs begins
searching for a string as soon as you type the first character.
As you type more characters, it refines the search.  @xref{Incremental Search}.

@item Indentation
Indentation means blank space at the beginning of a line.  Most
programming languages have conventions for using indentation to
illuminate the structure of the program, and Emacs has special
commands to adjust indentation.
@xref{Indentation}.

@item Indirect Buffer
An indirect buffer is a buffer that shares the text of another buffer,
called its base buffer (q.v.).  @xref{Indirect Buffers}.

@item Info
Info is the hypertext format used by the GNU project for writing
documentation.

@item Input Event
An input event represents, within Emacs, one action taken by the user on
the terminal.  Input events include typing characters, typing function
keys, pressing or releasing mouse buttons, and switching between Emacs
frames.  @xref{User Input}.

@item Input Method
An input method is a system for entering non-@acronym{ASCII} text characters by
typing sequences of @acronym{ASCII} characters (q.v.).  @xref{Input Methods}.

@item Insertion
Insertion means adding text into the buffer, either from the keyboard
or from some other place in Emacs.

@item Interlocking
@xref{Glossary---File Locking}.

@item Isearch
@xref{Glossary---Incremental Search}.

@item Justification
Justification means adding extra spaces within lines of text in order
to adjust the position of the text edges.  @xref{Fill Commands}.

@item Key Binding
@xref{Glossary---Binding}.

@item Keyboard Macro
Keyboard macros are a way of defining new Emacs commands from
sequences of existing ones, with no need to write a Lisp program.
You can use a macro to record a sequence of commands, then
play them back as many times as you like.
@xref{Keyboard Macros}.

@cindex keyboard shortcuts
@item Keyboard Shortcut
A keyboard shortcut is a key sequence (q.v.@:) that invokes a
command.  What some programs call ``assigning a keyboard shortcut'',
Emacs calls ``binding a key sequence''.  @xref{Glossary---Binding}.

@item Key Sequence
A key sequence (key, for short) is a sequence of input events (q.v.@:)
that are meaningful as a single unit.  If the key sequence is enough to
specify one action, it is a complete key (q.v.); if it is not enough,
it is a prefix key (q.v.).  @xref{Keys}.

@item Keymap
The keymap is the data structure that records the bindings (q.v.@:) of
key sequences to the commands that they run.  For example, the global
keymap binds the character @kbd{C-n} to the command function
@code{next-line}.  @xref{Keymaps}.

@item Keyboard Translation Table
The keyboard translation table is an array that translates the character
codes that come from the terminal into the character codes that make up
key sequences.

@item Kill Ring
The kill ring is where all text you have killed (@pxref{Glossary---Killing})
recently is saved.  You can reinsert any of the killed text still in
the ring; this is called yanking (q.v.).  @xref{Yanking}.

@anchor{Glossary---Killing}
@item Killing
Killing means erasing text and saving it on the kill ring so it can be
yanked (q.v.@:) later.  Some other systems call this ``cutting''.
Most Emacs commands that erase text perform killing, as opposed to
deletion (q.v.).  @xref{Killing}.

@item Killing a Job
Killing a job (such as, an invocation of Emacs) means making it cease
to exist.  Any data within it, if not saved in a file, is lost.
@xref{Exiting}.

@item Language Environment
Your choice of language environment specifies defaults for the input
method (q.v.@:) and coding system (q.v.).  @xref{Language
Environments}.  These defaults are relevant if you edit
non-@acronym{ASCII} text (@pxref{International}).

@c TODO?  Not really appropriate for the user manual I think.
@c Lexical Binding

@item Line Wrapping
@xref{Glossary---Filling}.

@item Lisp
Lisp is a programming language.  Most of Emacs is written in a dialect
of Lisp, called Emacs Lisp, which is extended with special features that
make it especially suitable for text editing tasks.

@item List
A list is, approximately, a text string beginning with an open
parenthesis and ending with the matching close parenthesis.  In C mode
and other non-Lisp modes, groupings surrounded by other kinds of matched
delimiters appropriate to the language, such as braces, are also
considered lists.  Emacs has special commands for many operations on
lists.  @xref{Moving by Parens}.

@item Local
Local means ``in effect only in a particular context''; the relevant
kind of context is a particular function execution, a particular
buffer, or a particular major mode.  It is the opposite of ``global''
(q.v.).  Specific uses of ``local'' in Emacs terminology appear below.

@item Local Abbrev
A local abbrev definition is effective only if a particular major mode
is selected.  In that major mode, it overrides any global definition
for the same abbrev.  @xref{Abbrevs}.

@item Local Keymap
A local keymap is used in a particular major mode; the key bindings
(q.v.@:) in the current local keymap override global bindings of the
same key sequences.  @xref{Keymaps}.

@item Local Variable
A local value of a variable (q.v.@:) applies to only one buffer.
@xref{Locals}.

@item @kbd{M-}
@kbd{M-} in the name of a character is an abbreviation for @key{Meta},
one of the modifier keys that can accompany any character.
@xref{User Input,M-}.

@item @kbd{M-C-}
@kbd{M-C-} in the name of a character is an abbreviation for
Control-Meta; it means the same thing as @kbd{C-M-} (q.v.).

@item @kbd{M-x}
@kbd{M-x} is the key sequence that is used to call an Emacs command by
name.  This is how you run commands that are not bound to key sequences.
@xref{M-x,M-x,Running Commands by Name}.

@anchor{Glossary---Mail}
@item Mail
Mail means messages sent from one user to another through the computer
system, to be read at the recipient's convenience.  Emacs has commands for
composing and sending mail, and for reading and editing the mail you have
received.  @xref{Sending Mail}.  @xref{Rmail}, for one way to read
mail with Emacs.

@item Mail Composition Method
A mail composition method is a program runnable within Emacs for editing
and sending a mail message.  Emacs lets you select from several
alternative mail composition methods.  @xref{Mail Methods}.

@item Major Mode
The Emacs major modes are a mutually exclusive set of options, each of
which configures Emacs for editing a certain sort of text.  Ideally,
each programming language has its own major mode.  @xref{Major Modes}.

@c FIXME: Mention margins for filling?
@item Margin
The space between the usable part of a window (including the
fringe) and the window edge.

@item Mark
The mark points to a position in the text.  It specifies one end of the
region (q.v.), point being the other end.  Many commands operate on
all the text from point to the mark.  Each buffer has its own mark.
@xref{Mark}.

@item Mark Ring
The mark ring is used to hold several recent previous locations of the
mark, in case you want to move back to them.  Each buffer has its
own mark ring; in addition, there is a single global mark ring (q.v.).
@xref{Mark Ring}.

@item Menu Bar
The menu bar is a line at the top of an Emacs frame.  It contains
words you can click on with the mouse to bring up menus, or you can use
a keyboard interface to navigate it.  @xref{Menu Bars}.

@item Message
@xref{Glossary---Mail}.

@item Meta
Meta is the name of a modifier bit which you can use in a command
character.  To enter a meta character, you hold down the @key{Meta}
key while typing the character.  We refer to such characters with
names that start with @kbd{Meta-} (usually written @kbd{M-} for
short).  For example, @kbd{M-<} is typed by holding down @key{Meta}
and at the same time typing @kbd{<} (which itself is done, on most
terminals, by holding down @key{SHIFT} and typing @kbd{,}).
@xref{User Input,Meta}.

On some terminals, the @key{Meta} key is actually labeled @key{Alt}
or @key{Edit}.

@item Meta Character
A Meta character is one whose character code includes the Meta bit.

@item Minibuffer
The minibuffer is the window that appears when necessary inside the
echo area (q.v.), used for reading arguments to commands.
@xref{Minibuffer}.

@anchor{Glossary---Minibuffer History}
@item Minibuffer History
The minibuffer history records the text you have specified in the past
for minibuffer arguments, so you can conveniently use the same text
again.  @xref{Minibuffer History}.

@item Minor Mode
A minor mode is an optional feature of Emacs, which can be switched on
or off independently of all other features.  Each minor mode has a
command to turn it on or off.  Some minor modes are global (q.v.),
and some are local (q.v.).  @xref{Minor Modes}.

@item Minor Mode Keymap
A minor mode keymap is a keymap that belongs to a minor mode and is
active when that mode is enabled.  Minor mode keymaps take precedence
over the buffer's local keymap, just as the local keymap takes
precedence over the global keymap.  @xref{Keymaps}.

@item Mode Line
The mode line is the line at the bottom of each window (q.v.), giving
status information on the buffer displayed in that window.  @xref{Mode
Line}.

@item Modified Buffer
A buffer (q.v.@:) is modified if its text has been changed since the
last time the buffer was saved (or since it was created, if it
has never been saved).  @xref{Saving}.

@item Moving Text
Moving text means erasing it from one place and inserting it in
another.  The usual way to move text is by killing (q.v.@:) it and then
yanking (q.v.@:) it.  @xref{Killing}.

@item MULE
@cindex MULE
Prior to Emacs 23, @acronym{MULE} was the name of a software package
which provided a @dfn{MULtilingual Enhancement} to Emacs, by adding
support for multiple character sets (q.v.).  @acronym{MULE} was later
integrated into Emacs, and much of it was replaced when Emacs gained
internal Unicode support in version 23.

Some parts of Emacs that deal with character set support still use the
@acronym{MULE} name.  @xref{International}.

@item Multibyte Character
A multibyte character is a character that takes up several bytes in a
buffer.  Emacs uses multibyte characters to represent non-@acronym{ASCII} text,
since the number of non-@acronym{ASCII} characters is much more than 256.
@xref{International Chars, International Characters}.

@item Named Mark
A named mark is a register (q.v.), in its role of recording a
location in text so that you can move point to that location.
@xref{Registers}.

@item Narrowing
Narrowing means creating a restriction (q.v.@:) that limits editing in
the current buffer to only a part of the text.  Text outside that part
is inaccessible for editing (or viewing) until the boundaries are
widened again, but it is still there, and saving the file saves it
all.  @xref{Narrowing}.

@item Newline
Control-J characters in the buffer terminate lines of text and are
therefore also called newlines.  @xref{Glossary---End Of Line}.

@cindex nil
@cindex t
@item @code{nil}
@code{nil} is a value usually interpreted as a logical ``false''.  Its
opposite is @code{t}, interpreted as ``true''.

@anchor{Glossary---Numeric Argument}
@item Numeric Argument
A numeric argument is a number, specified before a command, to change
the effect of the command.  Often the numeric argument serves as a
repeat count.  @xref{Arguments}.

@item Overwrite Mode
Overwrite mode is a minor mode.  When it is enabled, ordinary text
characters replace the existing text after point rather than pushing
it to one side.  @xref{Minor Modes}.

@item Package
A package is a collection of Lisp code that you download and
automatically install from within Emacs.  Packages provide a
convenient way to add new features.  @xref{Packages}.

@anchor{Glossary---Page}
@item Page
A page is a unit of text, delimited by formfeed characters (@acronym{ASCII}
control-L, code 014) at the beginning of a line.  Some Emacs
commands are provided for moving over and operating on pages.
@xref{Pages}.

@item Paragraph
Paragraphs are the medium-size unit of human-language text.  There are
special Emacs commands for moving over and operating on paragraphs.
@xref{Paragraphs}.

@item Parsing
We say that certain Emacs commands parse words or expressions in the
text being edited.  Really, all they know how to do is find the other
end of a word or expression.

@item Point
Point is the place in the buffer at which insertion and deletion
occur.  Point is considered to be between two characters, not at one
character.  The terminal's cursor (q.v.@:) indicates the location of
point.  @xref{Point}.

@item Prefix Argument
@xref{Glossary---Numeric Argument}.

@item Prefix Key
A prefix key is a key sequence (q.v.@:) whose sole function is to
introduce a set of longer key sequences.  @kbd{C-x} is an example of
prefix key; any two-character sequence starting with @kbd{C-x} is
therefore a legitimate key sequence.  @xref{Keys}.

@c I don't think this kind of thing needs to be here.
@ignore
@item Primary Rmail File
Your primary Rmail file is the file named @samp{RMAIL} in your home
directory.  That's where Rmail stores your incoming mail, unless you
specify a different file name.  @xref{Rmail}.
@end ignore

@item Primary Selection
The primary selection is one particular X selection (q.v.); it is the
selection that most X applications use for transferring text to and from
other applications.

The Emacs kill commands set the primary selection and the yank command
uses the primary selection when appropriate.  @xref{Killing}.

@item Prompt
A prompt is text used to ask you for input.  Displaying a prompt
is called prompting.  Emacs prompts always appear in the echo area
(q.v.).  One kind of prompting happens when the minibuffer is used to
read an argument (@pxref{Minibuffer}); the echoing that happens when
you pause in the middle of typing a multi-character key sequence is also
a kind of prompting (@pxref{Echo Area}).

@item Query-Replace
Query-replace is an interactive string replacement feature provided by
Emacs.  @xref{Query Replace}.

@anchor{Glossary---Quitting}
@item Quitting
Quitting means canceling a partially typed command or a running
command, using @kbd{C-g} (or @kbd{C-@key{BREAK}} on MS-DOS).  @xref{Quitting}.

@item Quoting
Quoting means depriving a character of its usual special significance.
The most common kind of quoting in Emacs is with @kbd{C-q}.  What
constitutes special significance depends on the context and on
convention.  For example, an ordinary character as an Emacs command
inserts itself; so in this context, a special character is any character
that does not normally insert itself (such as @key{DEL}, for example),
and quoting it makes it insert itself as if it were not special.  Not
all contexts allow quoting.  @xref{Inserting Text,Quoting}.

@item Quoting File Names
Quoting a file name turns off the special significance of constructs
such as @samp{$}, @samp{~} and @samp{:}.  @xref{Quoted File Names}.

@item Read-Only Buffer
A read-only buffer is one whose text you are not allowed to change.
Normally Emacs makes buffers read-only when they contain text which
has a special significance to Emacs; for example, Dired buffers.
Visiting a file that is write-protected also makes a read-only buffer.
@xref{Buffers}.

@item Rectangle
A rectangle consists of the text in a given range of columns on a given
range of lines.  Normally you specify a rectangle by putting point at
one corner and putting the mark at the diagonally opposite corner.
@xref{Rectangles}.

@item Recursive Editing Level
A recursive editing level is a state in which part of the execution of
a command involves asking you to edit some text.  This text may
or may not be the same as the text to which the command was applied.
The mode line indicates recursive editing levels with square brackets
(@samp{[} and @samp{]}).  @xref{Recursive Edit}.

@item Redisplay
Redisplay is the process of correcting the image on the screen to
correspond to changes that have been made in the text being edited.
@xref{Screen,Redisplay}.

@item Regexp
@xref{Glossary---Regular Expression}.

@item Region
The region is the text between point (q.v.@:) and the mark (q.v.).
Many commands operate on the text of the region.  @xref{Mark,Region}.

@item Register
Registers are named slots in which text, buffer positions, or
rectangles can be saved for later use.  @xref{Registers}.  A related
Emacs feature is bookmarks (q.v.).

@anchor{Glossary---Regular Expression}
@item Regular Expression
A regular expression is a pattern that can match various text strings;
for example, @samp{a[0-9]+} matches @samp{a} followed by one or more
digits.  @xref{Regexps}.

@item Remote File
A remote file is a file that is stored on a system other than your own.
Emacs can access files on other computers provided that they are
connected to the same network as your machine, and (obviously) that
you have a supported method to gain access to those files.
@xref{Remote Files}.

@item Repeat Count
@xref{Glossary---Numeric Argument}.

@item Replacement
@xref{Glossary---Global Substitution}.

@item Restriction
A buffer's restriction is the amount of text, at the beginning or the
end of the buffer, that is temporarily inaccessible.  Giving a buffer a
nonzero amount of restriction is called narrowing (q.v.); removing
a restriction is called widening (q.v.).  @xref{Narrowing}.

@item @key{RET}
@key{RET} is a character that in Emacs runs the command to insert a
newline into the text.  It is also used to terminate most arguments
read in the minibuffer (q.v.).  @xref{User Input,Return}.

@item Reverting
Reverting means returning to the original state.  Emacs lets you
revert a buffer by re-reading its file from disk.  @xref{Reverting}.

@c Seems too obvious, also there is nothing special about the format
@c these days.
@ignore
@item Rmail File
An Rmail file is a file containing text in the format used by
Rmail for storing mail.  @xref{Rmail}.
@end ignore

@item Saving
Saving a buffer means copying its text into the file that was visited
(q.v.@:) in that buffer.  This is the way text in files actually gets
changed by your Emacs editing.  @xref{Saving}.

@item Scroll Bar
A scroll bar is a tall thin hollow box that appears at the side of a
window.  You can use mouse commands in the scroll bar to scroll the
window.  The scroll bar feature is supported only under windowing
systems.  @xref{Scroll Bars}.

@item Scrolling
Scrolling means shifting the text in the Emacs window so as to see a
different part of the buffer.  @xref{Scrolling}.

@item Searching
Searching means moving point to the next occurrence of a specified
string or the next match for a specified regular expression.
@xref{Search}.

@item Search Path
A search path is a list of directory names, to be used for searching for
files for certain purposes.  For example, the variable @code{load-path}
holds a search path for finding Lisp library files.  @xref{Lisp Libraries}.

@item Secondary Selection
The secondary selection is one particular X selection (q.v.); some X
applications can use it for transferring text to and from other
applications.  Emacs has special mouse commands for transferring text
using the secondary selection.  @xref{Secondary Selection}.

@item Selected Frame
The selected frame is the one your input currently operates on.
@xref{Frames}.

@item Selected Window
The selected window is the one your input currently operates on.
@xref{Basic Window}.

@item Selecting a Buffer
Selecting a buffer means making it the current (q.v.@:) buffer.
@xref{Select Buffer}.

@item Selection
Windowing systems allow an application program to specify
selections whose values are text.  A program can also read the
selections that other programs have set up.  This is the principal way
of transferring text between window applications.  Emacs has commands to
work with the primary (q.v.@:) selection and the secondary (q.v.@:)
selection, and also with the clipboard (q.v.).

@item Self-Documentation
Self-documentation is the feature of Emacs that can tell you what any
command does, or give you a list of all commands related to a topic
you specify.  You ask for self-documentation with the help character,
@kbd{C-h}.  @xref{Help}.

@item Self-Inserting Character
A character is self-inserting if typing that character inserts that
character in the buffer.  Ordinary printing and whitespace characters
are self-inserting in Emacs, except in certain special major modes.

@item Sentences
Emacs has commands for moving by or killing by sentences.
@xref{Sentences}.

@anchor{Glossary---Server}
@item Server
Within Emacs, you can start a ``server'' process, which listens for
connections from ``clients''.  This offers a faster alternative to
starting several Emacs instances.  @xref{Emacs Server}, and
@ref{Glossary---Daemon}.

@c This is only covered in the lispref, not the user manual.
@ignore
@item Session Manager
Some window systems (q.v.@:) provide a tool called a ``session manager''.
This offers the ability to save your windows when you log off,
and restore them after you log in again.
@end ignore

@item Sexp
A sexp (short for ``s-expression'') is the basic syntactic unit of
Lisp in its textual form: either a list, or Lisp atom.  Sexps are also
the balanced expressions (q.v.@:) of the Lisp language; this is why
the commands for editing balanced expressions have @samp{sexp} in their
name.  @xref{Expressions,Sexps}.

@item Simultaneous Editing
Simultaneous editing means two users modifying the same file at once.
Simultaneous editing, if not detected, can cause one user to lose his
or her work.  Emacs detects all cases of simultaneous editing, and
warns one of the users to investigate.
@xref{Interlocking,Interlocking,Simultaneous Editing}.

@item @key{SPC}
@key{SPC} is the space character, which you enter by pressing the
space bar.

@item Speedbar
The speedbar is a special tall frame that provides fast access to Emacs
buffers, functions within those buffers, Info nodes, and other
interesting parts of text within Emacs.  @xref{Speedbar}.

@item Spell Checking
Spell checking means checking correctness of the written form of each
one of the words in a text.  Emacs can use various external
spelling-checker programs to check the spelling of parts of a buffer
via a convenient user interface.  @xref{Spelling}.

@item String
A string is a kind of Lisp data object that contains a sequence of
characters.  Many Emacs variables are intended to have strings as
values.  The Lisp syntax for a string consists of the characters in the
string with a @samp{"} before and another @samp{"} after.  A @samp{"}
that is part of the string must be written as @samp{\"} and a @samp{\}
that is part of the string must be written as @samp{\\}.  All other
characters, including newline, can be included just by writing them
inside the string; however, backslash sequences as in C, such as
@samp{\n} for newline or @samp{\241} using an octal character code, are
allowed as well.

@item String Substitution
@xref{Glossary---Global Substitution}.

@item Syntax Highlighting
@xref{Glossary---Font Lock}.

@item Syntax Table
The syntax table tells Emacs which characters are part of a word,
which characters balance each other like parentheses, etc.
@xref{Syntax Tables,, Syntax Tables, elisp, The Emacs Lisp Reference
Manual}.

@item Super
Super is the name of a modifier bit that a keyboard input character may
have.  To make a character Super, type it while holding down the
@key{SUPER} key.  Such characters are given names that start with
@kbd{Super-} (usually written @kbd{s-} for short).  @xref{User Input}.

@item Suspending
Suspending Emacs means stopping it temporarily and returning control
to its parent process, which is usually a shell.  Unlike killing a job
(q.v.), you can later resume the suspended Emacs job without losing
your buffers, unsaved edits, undo history, etc.  @xref{Exiting}.

@item @key{TAB}
@key{TAB} is the tab character.  In Emacs it is typically used for
indentation or completion.

@anchor{Glossary---Tags Table}
@item Tags Table
A tags table is a file that serves as an index to the function
definitions in one or more other files.  @xref{Tags}.

@item Termscript File
A termscript file contains a record of all characters sent by Emacs to
the terminal.  It is used for tracking down bugs in Emacs redisplay.
Emacs does not make a termscript file unless you tell it to.
@xref{Bugs}.

@item Text
``Text'' has two meanings (@pxref{Text}):

@itemize @bullet
@item
Data consisting of a sequence of characters, as opposed to binary
numbers, executable programs, and the like.  The basic contents of an
Emacs buffer (aside from the text properties, q.v.@:) are always text
in this sense.
@item
Data consisting of written human language (as opposed to programs),
or following the stylistic conventions of human language.
@end itemize

@anchor{Glossary---Text Terminal}
@item Text Terminal
A text terminal, or character terminal, is a display that is limited
to displaying text in character units.  Such a terminal cannot control
individual pixels it displays.  Emacs supports a subset of display
features on text terminals.

@item Text Properties
Text properties are annotations recorded for particular characters in
the buffer.  Images in the buffer are recorded as text properties;
they also specify formatting information.  @xref{Editing Format Info}.

@item Theme
A theme is a set of customizations (q.v.@:) that give Emacs a
particular appearance or behavior.  For example, you might use a theme
for your favorite set of faces (q.v.).

@item Tool Bar
The tool bar is a line (sometimes multiple lines) of icons at the top
of an Emacs frame.  Clicking on one of these icons executes a command.
You can think of this as a graphical relative of the menu bar (q.v.).
@xref{Tool Bars}.

@anchor{Glossary---Tooltips}
@item Tooltips
Tooltips are small windows displaying a help echo (q.v.@:) text, which
explains parts of the display, lists useful options available via mouse
clicks, etc.  @xref{Tooltips}.

@item Top Level
Top level is the normal state of Emacs, in which you are editing the
text of the file you have visited.  You are at top level whenever you
are not in a recursive editing level (q.v.@:) or the minibuffer
(q.v.), and not in the middle of a command.  You can get back to top
level by aborting (q.v.@:) and quitting (q.v.).  @xref{Quitting}.

@item Transient Mark Mode
The default behavior of the mark (q.v.@:) and region (q.v.), in which
setting the mark activates it and highlights the region, is called
Transient Mark mode.  In GNU Emacs 23 and onwards, it is enabled by
default.  @xref{Disabled Transient Mark}.

@item Transposition
Transposing two units of text means putting each one into the place
formerly occupied by the other.  There are Emacs commands to transpose
two adjacent characters, words, balanced expressions (q.v.@:) or lines
(@pxref{Transpose}).

@item Trash Can
@xref{Glossary---Deletion of Files}.

@anchor{Glossary---Truncation}
@item Truncation
Truncating text lines in the display means leaving out any text on a
line that does not fit within the right margin of the window
displaying it.  @xref{Continuation Lines,Truncation}, and
@ref{Glossary---Continuation Line}.

@item TTY
@xref{Glossary---Text Terminal}.

@item Undoing
Undoing means making your previous editing go in reverse, bringing
back the text that existed earlier in the editing session.
@xref{Undo}.

@item Unix
Unix is a class of multi-user computer operating systems with a long
history.  There are several implementations today.  The GNU project
(q.v.@:) aims to develop a complete Unix-like operating system that
is free software (q.v.).

@item User Option
A user option is a face (q.v.@:) or a variable (q.v.@:) that exists so
that you can customize Emacs by setting it to a new value.
@xref{Easy Customization}.

@item Variable
A variable is an object in Lisp that can store an arbitrary value.
Emacs uses some variables for internal purposes, and has others (known
as ``user options''; q.v.@:) just so that you can set their values to
control the behavior of Emacs.  The variables used in Emacs that you
are likely to be interested in are listed in the Variables Index in
this manual (@pxref{Variable Index}).  @xref{Variables}, for
information on variables.

@item Version Control
Version control systems keep track of multiple versions of a source file.
They provide a more powerful alternative to keeping backup files (q.v.).
@xref{Version Control}.

@item Visiting
Visiting a file means loading its contents into a buffer (q.v.@:)
where they can be edited.  @xref{Visiting}.

@item Whitespace
Whitespace is any run of consecutive formatting characters (space,
tab, newline, and backspace).

@item Widening
Widening is removing any restriction (q.v.@:) on the current buffer;
it is the opposite of narrowing (q.v.).  @xref{Narrowing}.

@item Window
Emacs divides a frame (q.v.@:) into one or more windows, each of which
can display the contents of one buffer (q.v.@:) at any time.
@xref{Screen}, for basic information on how Emacs uses the screen.
@xref{Windows}, for commands to control the use of windows.  Some
other editors use the term ``window'' for what we call a ``frame''
(q.v.@:) in Emacs.

@item Window System
A window system is software that operates on a graphical display
(q.v.), to subdivide the screen so that multiple applications can
have their] own windows at the same time.  All modern operating systems
include a window system.

@item Word Abbrev
@xref{Glossary---Abbrev}.

@item Word Search
Word search is searching for a sequence of words, considering the
punctuation between them as insignificant.  @xref{Word Search}.

@anchor{Glossary---Yanking}
@item Yanking
Yanking means reinserting text previously killed (q.v.).  It can be
used to undo a mistaken kill, or for copying or moving text.  Some
other systems call this ``pasting''.  @xref{Yanking}.
@end table