demoeffect n.
[demoscene] What among hackers
is called a display hack.
Classical effects include "plasma" (colorful mess), "keftales"
(x*x+y*y and other similar patterns, usually combined with
color-cycling), realtime fractals, realtime 3d graphics, etc.
Historically, demo effects have cheated as much as possible to
gain more speed and more complexity, using low-precision math and
masses of assembler code and building animation realtime are
three common tricks, but use of special hardware to fake effects
is a Good Thing on the
demoscene (though this is becoming less common as platforms like
the Amiga fade away).