Poker is a type of card game in which players bet on the value of the card combination ("hand") in their possession, by placing a bet into a central pot. The winner is the one who holds the hand with the highest value according to an established hand rankings hierarchy, or otherwise the player who remains in the hand after all others have folded (the player who makes an un-called bet), and wins the current pot.

Variations

Poker has many variations, all following a similar pattern of play and using the same hand ranking hierarchy. There are three main families of variants, largely grouped by the protocol of card-dealing and betting:

• "Straight" - A complete hand is dealt to each player, and players bet in one round, with raising and re-raising allowed. This is the oldest poker family; the root of the game as currently played was a game known as Primero, which evolved into the game Three-card brag, a very popular gentleman's game around the time of the American Revolutionary War and still enjoyed in the U.K. today. "Straight" hands of five cards are sometimes used as a final showdown, but poker is currently virtually always played in a more complex form to allow for additional strategy.
• Stud - Cards are dealt in a prearranged combination of face-down and face-up rounds or "streets", with a round of betting following each. This is the next-oldest family; as poker progressed from three to five-card hands, they were often dealt one card at a time, either face-down or face-up, with a betting round between each. The most popular stud variant today, 7 card stud, deals two extra cards to each player (three facedown, four faceup) from which they must make the best possible 5-card hand.
• Draw - A complete hand is dealt to each player, face-down, and after betting, players are allowed to attempt to change their hand by discarding unwanted cards and being dealt new ones. 5 card draw is the most famous variation in this family.
• Community - A variation of Stud, players are dealt an incomplete hand of face-down cards, and then a number of face-up "community" cards are dealt to the center of the table, each of which can be used by one or more of the players to make a 5-card hand. Texas hold-em and Omaha are two well-known variants of the Community family.

Other games that use poker hand rankings may likewise be referred to as "poker". Video poker is a single-player computer game that functions much like a slot machine; most video poker machines play draw poker, where the player bets, a hand is dealt, and the player can discard and replace cards. Payout is dependent on the hand resulting after the draw and the player's initial bet.

Another game with the "Poker" name, but with a vastly different mode of play, is called "Acey-Deucey" or "Red Dog" Poker. This game is more similar to Blackjack in its layout and betting; each player bets against the house, and then is dealt two cards. For the player to win, the third card dealt (after an opportunity to raise the bet) must have a value in between the first two. Payout is based on the odds that this is possible, based on the difference in values of the first two cards.