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

talker system
 n.

    British hackerism for software that enables real-time chat or talk mode.


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

talk
talker system

    A Unix program and
   protocol supporting conversation between two or more users
   who may be logged into the same computer or different
   computers on a network.  Variants include ntalk, ytalk,
   and ports or emulators of these programs for other
   platforms.

   Unix has the talk program and protocol and its variants
   xtalk and ytalk for the X Window System; VMS has
   phone; Windows for Workgroups has chat.  ITS also has
   a talk system.  These split the screen into separate areas for
   each user.

   Unix's write command can also be used, though it does not
   attempt to separate input and output on the screen.

   Users of such systems are said to be in talk mode which has
   many conventional abbreviations and idioms.  Most of these
   survived into chat jargon, but many fell out of common use
   with the migration of user prattle from talk-like systems to
   chat systems in the early 1990s.  These disused
   talk-specific forms include:

   "BYE?" - are you ready to close the conversation?  This is the
   standard way to end a talk-mode conversation; the other person
   types "BYE" to confirm, or else continues the conversation.

   "JAM"/"MIN" - just a minute

   "O" - "over" (I have stopped talking).  Also "/" as in x/y - x
   over y, or two newlines (the latter being the most common).

   "OO" - "over and out" - end of conversation.

   "\" - Greek lambda.

   "R U THERE?" - are you there?

   "SEC" - wait a second.

   "/\/\/" - laughter.  But on a MUD, this usually means
   "earthquake fault".

   See also talk bomb.

   (1998-01-25)