3-BET
The first reraise preflop. The term originated with limit hold'em. The first raise preflop is often announced as "two bets" and the next raise is thus "three bets". This got adopted in no-limit as a "3-bet".
4-BET
A raise of a 3-bet. We'll stop now.
6-MAX
A 6-seated game of poker, common for online cash games.
