Source : Free On-Line Dictionary of Computing

display hack
     
         A program with the same approximate purpose as a
        kaleidoscope: to make pretty pictures.  Famous display hacks
        include {munching squares}, {smoking clover}, the {BSD Unix}
        "rain(6)" program, "worms(6)" on miscellaneous Unixes, and the
        {X} "kaleid(1)" program.  Display hacks can also be
        implemented without programming by creating text files
        containing numerous escape sequences for interpretation by a
        video terminal; one notable example displayed, on any VT100, a
        Christmas tree with twinkling lights and a toy train circling
        its base.  The {hack value} of a display hack is proportional
        to the aesthetic value of the images times the cleverness of
        the algorithm divided by the size of the code.  Synonym
        {psychedelicware}.
     
        [{Jargon File}]
     
        (1995-05-10)