Poker is a card game in which players wager money, called the pot, on the outcome of a hand. Its rules vary from one form of the game to another, but all forms share certain essential features. The game may involve more than two people, but in most games only a single player is required to place a compulsory bet at the beginning of each round (called the ante or blind). Additional forced bets may be placed by players during the course of the hand on the basis of expected value. These bets may be made by a player holding a superior hand or by bluffing, in which case other players may call or fold.

A winning poker hand comprises five cards. The higher the card ranking, the more valuable the hand. A pair is two matching cards of the same rank, while a full house contains three matching cards of one rank and 2 matching cards of another rank. A flush is 5 consecutive cards of the same suit. A straight is five cards in sequence but of different suits. A three of a kind is 3 matching cards of one rank and two unmatched cards, while a two pair consists of two pairs of equal cards.

The value of a poker hand depends on the frequency with which it appears in the cards, the number of outs, and the relative strength of other hands. The player with the highest-ranked hand wins the pot. Other players may also win the pot by bluffing, in which they try to convince other players that they hold a better hand than they actually do.