It's basically a thing that tells you if you have a life or not. The higher the rating, the less likely you have a life. Or so I have been told. The only way to raise the steam rating is to play more steam games.
Anyways, SCII has been crashing on me a lot lately. After a couple to a few epic battles, I get a out of memory crash (core and graphics (switches between the two)). I am getting quite annoyed of this. I ran Memtest, P95, hdtune. and furmark for 30 min - 8 hours (depending on the program), and found no errors. Only happens on SCII too.