Function: server-mode

Toggle Server mode.
With a prefix argument ARG, enable Server mode if ARG is
positive, and disable it otherwise. If called from Lisp, enable
Server mode if ARG is omitted or nil.

Server mode runs a process that accepts commands from the
`emacsclient' program. See Info node `Emacs server' and
`server-start' for details. (fn &optional ARG)

Variable: server-mode

Non-nil if Server mode is enabled.
See the command `server-mode' for a description of this minor mode.
Setting this variable directly does not take effect;
either customize it (see the info node `Easy Customization')
or call the function `server-mode'.