Anti-Aliasing is the technique of minimizing aliasing when representing a high-resolution signal at a lower resolution.
In most cases, anti-aliasing means removing data at too high a frequency to represent.

Basicly, it makes images come out clearer and smoother to make it easy on your pretty eyesz

[This message has been edited by MaximusDecimus (edited 12-08-2005 @ 11:14 PM).]

AA is a hardware/software technique for reducing the jagglies that make some lines drawn on the screen look 'smoother'. It does this by giving shades of gray (or color) to the edges of the 'stairstep' transitions. This makes the jagged line look smoother, but the cost is fuzziness... it looks a little blurry. In RTW, the big issue for many players is graphic card and CPU power... using AA can take about 3 to 9% in resources when enabled, typically. If you run a higher resolutions, at least 1024x768 on CRT monitors, then IMHO it is often not worth the tradeoff... I personally keep it off. You will sometimes see AA called oversampling.

Also, if turned 'on' it may prevent you to obtain screenshots other than black pages

It does too, my last 45 SSs are all pitch black.

Here is more SS info. A 3rd party SS program line HyperSnap does not have the AA black screen issue.

About AA, here is an example of a close up, and the blurring that is part of general AA. Certain patterns, like mandlebrots and receeding horizon digital images benefit greatly from AA, esp. in reduging the moire-like image defects and improving the 'eyeball' view of the image.

Top: Digitally drawn line.
Bottom: Anti-aliased line.