Terminal-Specific - GNU Emacs Lisp Reference Manual

Each terminal type can have its own Lisp library that Emacs loads when run on that type of terminal. The library's name is constructed by concatenating the value of the variable term-file-prefix and the terminal type (specified by the environment variable TERM). Normally, term-file-prefix has the value "term/"; changing this is not recommended. Emacs finds the file in the normal manner, by searching the load-path directories, and trying the `.elc' and `.el' suffixes.

The usual function of a terminal-specific library is to enable special keys to send sequences that Emacs can recognize. It may also need to set or add to function-key-map if the Termcap or Terminfo entry does not specify all the terminal's function keys. See Terminal Input.

When the name of the terminal type contains a hyphen, and no library is found whose name is identical to the terminal's name, Emacs strips from the terminal's name the last hyphen and everything that follows it, and tries again. This process is repeated until Emacs finds a matching library or until there are no more hyphens in the name (the latter means the terminal doesn't have any library specific to it). Thus, for example, if there are no `aaa-48' and `aaa-30' libraries, Emacs will try the same library term/aaa.el for terminal types `aaa-48' and `aaa-30-rv'. If necessary, the library can evaluate (getenv "TERM") to find the full name of the terminal type.

Your init file can prevent the loading of the terminal-specific library by setting the variable term-file-prefix to nil. This feature is useful when experimenting with your own peculiar customizations.

You can also arrange to override some of the actions of the terminal-specific library by setting the variable term-setup-hook. This is a normal hook which Emacs runs using run-hooks at the end of Emacs initialization, after loading both your init file and any terminal-specific libraries. You can use this variable to define initializations for terminals that do not have their own libraries. See Hooks.

— Variable: term-file-prefix

If the term-file-prefix variable is non-nil, Emacs loads a terminal-specific initialization file as follows:
          (load (concat term-file-prefix (getenv "TERM")))
     
You may set the term-file-prefix variable to nil in your init file if you do not wish to load the terminal-initialization file. To do this, put the following in your init file: (setq term-file-prefix nil).
On MS-DOS, if the environment variable TERM is not set, Emacs uses `internal' as the terminal type.

— Variable: term-setup-hook

This variable is a normal hook that Emacs runs after loading your init file, the default initialization file (if any) and the terminal-specific Lisp file.
You can use term-setup-hook to override the definitions made by a terminal-specific file.

39.1.3 Terminal-Specific Initialization