WordNet (r) 3.0 (2006):

log off
    v 1: exit a computer; "Please log off before you go home" [syn:
         log out, log off] [ant: log in, log on, log-in]

The Free On-line Dictionary of Computing (30 December 2018):

log out
log off

    (Or "log off") To end an authenticated session,
   undoing what happens when you log in.  This is primarily to
   prevent other users gaining access to your logged in session,
   e.g. at an unattended computer, but typically also terminates
   any processes and network connections started as part of your
   session.

   (2004-11-16)