FPS = Frames Per Second, or how many frames (images) per second the GPU can create.
As a general rule, a LCD can show up to 60 Frames every second, so thats the baseline requirement FPS is measured against. The closer the FPS count is to 60, the smoother the gameplay is. The lower the number, the fewer frames are shown, and the more jerky the game appears.
As a general rule, having FPS that remains stable is prefered over FPS that jumps. IE: If FPS is stable at around 30 or so, games are quite playable. But if FPS jumps from a high of 45 to a low of 15, then parts of the game may be unplayable, even if the average is higher then 30 FPS or so.
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AA = Anti Alising, which is a method a reducing how jagged an image looks. A moniter is basically made up of individual pixels (think of them as squares, for simplicities sake). As such, you can't make a perfectly stright line except when going exactly horizontal/vertical, so all images look somewhat jagged around the edges. AA basically uses extra CPU power to try and make individual images less jagged.
Heres a decent example:
The second daimond used anti-alising to smooth the edges out.