I only googled 'lol' last week as well.
There's several internet slang definitions but the most popular is 'laughing out loud'.
lmao (LMAO) is another I'd seen, this means 'laughing my ass off'.
To catch up with the times, check out
http://www.internetslang.com/default.asp
rofl lmao funny omg haha lmfao wtf lawl roflmao laugh lolz