When Emacs exits, it terminates all its subprocesses. For
subprocesses that run a program, it sends them the
signal; connections are simply closed. Because subprocesses may be
doing valuable work, Emacs normally asks the user to confirm that it
is ok to terminate them. Each process has a query flag, which, if
nil, says that Emacs should ask for confirmation before
exiting and thus killing that process. The default for the query flag
t, meaning do query.