FSAA = Full Screen Anti Aliasing
It's a multisampling technique that 3d cards can do to reduce "jagging" on edges. In other words, it makes the outlines of the 3d stuff more smooth and nice. The number after the FSAA setting (ie. 0, 2, 4 etc) refers to how many samples per pixel the card will do. The more samples, the nicer looking graphics but also the more samples, the slower the game will render.
In BD I guess it only really affects the characters though..
- Telemachos