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}.


Source: The Jargon File