Poker is a popular card game that combines elements of chance and strategy. There are various styles of poker, all of which share an objective of presenting the least probable or highest-scoring hand. A poker hand is a configuration of five cards, either held entirely by a player or drawn partly from a number of shared, community cards. Players bet on their hands in a number of rounds as cards are drawn, employing various mathematical and intuitive strategies in an attempt to better opponents.
Given the game's many different forms and various dynamics, poker strategy becomes a complex subject. This article attempts to introduce only the basic strategy concepts.
Texas hold 'em (also known as hold 'em or holdem) is a variation of the standard card game of poker. Texas hold 'em consists of two cards being dealt face down to each player and then five community cards being placed face-up by the dealer — a series of three ("the flop") then an additional single card ("the turn" or "fourth) and another additional card ("the river" or fifth street") - with players having the option to check, bet, raise or fold after each deal; i.e., betting may occur prior to the flop, "on the flop", "on the turn", and "on the river". Texas Hold 'em is the "H" game featured in H.O.R.S.E and in H.O.S.E.
Draw poker is any poker variant in which each player is dealt a complete hand before the first betting round, and then develops the hand for later rounds by replacing, or "drawing", cards.
The descriptions below assume the reader is familiar with the general game play of poker, and with hand values (both high and low variations). They also make no assumptions about what betting structure is used. In home games, it is typical to use an ante, and betting always begins with the player to the dealer's left. In casino play, it is more common to use blinds; the first betting round thus begins with the player to the left of the big blind, and subsequent rounds begin with the player to the dealer's left, thus draw games are very positional.
In poker, pot odds are the ratio of the current size of the pot to the cost of a contemplated call. Pot odds are often compared to the probability of winning a hand with a future card in order to estimate the call's expected value.
Morton's theorem is a poker principle articulated by Andy Morton in a Usenet poker newsgroup. It states that in multi-way pots, a player's expectation may be maximized by an opponent making a correct decision.
The most common application of Morton's theorem occurs when one player holds the best hand, but there are two or more opponents on draws. In this case, the player with the best hand might make more money in the long run when an opponent folds to a bet, even if that opponent is folding correctly and would be making a personal mistake to call the bet. This type of situation is sometimes referred to as implicit collusion.