server-mode
server-mode is an interactive autoloaded compiled Lisp function in `server.el
'.
(server-mode &optional ARG)
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.