The Jargon File (version 4.4.7, 29 Dec 2003):

comm mode
 /kom mohd/, n.

    [ITS: from the feature supporting on-line chat; the first word may be
    spelled with one or two m's] Syn. for talk mode.


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

comm mode

    (Or "com mode") An ITS feature supporting interactive
   on-line chat.

   [Jargon File]

   (1998-01-18)