Heads-up poker is a form of poker that is played between only two players. It might be played during a larger cash game session, where the game is breaking up and only two players remain on the table, or where two players are trying to start a game and playing heads-up while waiting for other opponents.
Poker is a game that can be played with up to 10 players in some formats, but you only need a minimum of two people to play the game. A poker game involving two players is called a heads-up poker game. The positions in a heads-up poker game might be different than they are in a game with three or more players.