Originally posted by: Zugzwang152
basically anisotropic filtering is making things that are tilted on the z axis look clearer. Think of the scrolling text at the beginning of Star Wars movies... with anisotropic filtering, you could read the text longer as it scrolls up and gets squeezed to nothingness.
^^^ This is probably the easiest explanation one could come up with.
Imagine standing on a street, staring straight ahead toward the horizon. If you look carefully at the ground ahead of you, you will notice "zones" of clarity in the textures. For example, from your feet to about 30 feet ahead the ground looks the most clear and sharp. From 30 ft to 100 ft, the ground looks medium clarity and just a tiny bit sharp. From 100 ft to the horizon, the ground looks like a blurry mess.
Anisotropic filtering removes these "zones" and helps create a smooth transition of texture levels (also known as Mip levels) from your feet to the horizon. Depending on the level of filtering applied, these zones will effectively be pushed back or completely eliminated, resulting in a sharp texture that looks much more realistic.
This is just a common example. It works the same for walls, ceilings, and pretty much everything that isn't perpendicular to your viewpoint. There are nuances from one video card to another, like sample patterns and "tap" levels, that affects overall picture quality, but we don't need to get into that.