The basics:
VPIP (Voluntarily put into pot): This is a percentage that shows how often this player pays to see flops. The precise % that make a player loose or tight will vary from game to game, but my general thoughts for 9/10-handed games are that 10% or less is a very tight player. ~15% is solid. 20% is probably about average for your opponents, and 30%+ starts to get pretty loose.
PFR (Preflop Raise): This is a percentage that shows how often a player raises preflop. A tight aggressive player might have VPIP and PFR of 11/8 -- meaning if they are going to enter the pot -- they will probably raise. They're probably only limping in position to set mine or with drawing hands... On the other hand, a loose aggressive guy might be 30/20. Where this stat saves (and makes) me the most money is when someone has a stat like 50/1 -- this guy loves to limp into pots so you'd be tempted to not give him credit for a hand, but if he's raising he has a monster.
AF (Aggression factor): This is a measure of how likely someone is to raise or check vs call. Someone with a high aggression factor isn't going to be calling often -- he'll bet, check, raise, or fold instead. I actually don't use this one anymore, I prefer AFq (aggression frequency). That stat is more of an indication of how often a player is betting/raising. Lets say you flop a set and your opponent has a high AF. You might be tempted to slowplay it thinking he will be betting often -- but many players with high AFs aren't maniacs -- they'll often check behind to try and improve (and checking doesnt lower AF). If your opponent has a high AFq -- you can comfortably check knowing he will likely build your pot for you...
As far as a FAQ, there doesn't seem to be one on this site. There are a couple of threads on 2+2 that go into more detail:
http://archives1.twoplustwo.com/showfla ... er=4946669http://forumserver.twoplustwo.com/35/mi ... ts-165898/