Heads up

From PokerWiki

Heads up (or heads-up) is a poker term indicating that only two players are playing. This happens in one of two cases:

• A heads up tournament or heads up table is a game which has only two players when it starts. Some online sites now offer heads-up tables where any two players can sit down and begin playing. A heads-up tournament is one like the National Heads-Up Poker Championship, where each game consists only of two players, and the winner of each game then moves up a bracket, usually using standard single-elimination rules.
• A hand at a poker table becomes heads up when all except two players fold. This can happen at any stage in a hand: preflop, on the flop, or later. Often the dealer will announce when a hand becomes heads up. Sometimes, brick-and-mortar casinos have different betting rules when a hand becomes head up (in particular, there is often no longer a cap once the hand becomes heads up).