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

display hack
 n.

    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 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 esthetic value of the
    images times the cleverness of the algorithm divided by the size of the
    code. Syn. psychedelicware.


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

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)