This article is from the sci.fractals FAQ, by Michael C. Taylor and Jean-Pierre Louvet with numerous contributions by others.
In computer graphics circles, "aliasing" refers to the
phenomenon of a high frequency in a continuous signal masquerading as
a lower frequency in the sampled output of the continuous signal. This
is a consequence of the discrete sampling used by the computer.
Put another way, it is the appearance of "chuckiness" in an still
image. Because of the finite resolution of a computer screen, a single
pixel has an associate width, whereas in mathematics each point is
infintesimely small, with "no width". So a single pixel on the screen
actually visually represents an infinite number of mathematical
points, each of which may have a different correct visual