FPS is Frames Per Second in this case. The higher the frames per second the smoother the game moves, so higher is better. You are getting a good amount of fps, considering the eye can't see past 60.
The other FPS is of course First Person Shooter, which is what CS:S (Counter-Strike:Source) is.
(If I am wrong, please correct me)
If you are playing online, the main thing you would have to worry about is Ping, which is basically how good of a connection you have. The lower the number, the better.