Source : Free On-Line Dictionary of Computing

ntalk
     
         ("new talk") An update of the {Unix} "{talk}" program,
        old versions of "talk" being referred to as "old talk".  New
        talk and old talk are generally incompatible, and attempts to
        get them to communicate result in entirely unhelpful error
        messages.
     
        On most modern {Unix} systems, the program "talk" is new talk,
        with some {SunOS} versions being a notable and annoying
        exception to this.
     
        (1997-09-11)