Source : Free On-Line Dictionary of Computing

well-known port
     
         A {TCP or {UDP} {port} with a number in the range
        0-1023 (originally 0-255).  The well-known port numbers are
        assigned by the {IANA} and on most systems can only be used by
        system (or root) processes or by programs executed by
        privileged users.
     
        (2002-10-06)