A starfield, in
computer graphics, is an effect that simulates stars. In its simplest form, white
pixels move across the screen at a
uniform speed, or move out from the center of the screen at a uniform speed. This looks
dumb.
In more
realistic starfields, stars move at different speeds, depending on "distance". They are also colored differently, depending on distance.
A really
advanced system just does all the calculations in
3d, so that you can move around in a starfield arbitrarily. This isn't too
accurate to reality (TM), since you would have to be moving at several times
the speed of light to see this, but it's what people expect.
If you want even more fake realism,
stars can become
streaks when they move really fast. This is simple; just draw a line between the last position of a star and its current position. Also, it is possible to add various other things that might be found in space, such as
nebulae, but that is
non-trivial.