These are acronyms that you'll see often in posts ITF (In this Forum). If you think of one that should be added, or run in to one that isn't on the list, please post ITT (In This Thread), and we'll add it.

2p - Two Pair
3-bet - A re-raise. The third bet on a given street
3b - 3-bet
3! - 3-bet
4-bet - a re-re-raise. The fourth bet on a given street
5-bet - come on. You get the pattern.
o - (eg JTo) The cards are not suited