Poker is played throughout the world, but it is most popular in its country of origin, the USA. Poker is a five-card vying game, played with standard playing-cards.

 A vying game is one where, instead of playing their cards out, the players bet as to who holds the best card combination by progressively raising the stakes until either there is a showdown, when the best hand wins all the stakes, or all but one player have given up betting and dropped out of play, when the last person to raise wins the pot without a showdown. Poker is therefore possible for the pot to be won by a hand that is not in fact the best, everyone else having been bluffed out of play. One of Poker's earliest names was, in fact, ‘Bluff’. Bluffing is as essential to vying as finessing is to trick-play.
A five-card vying game is one where, no matter how many cards may be dealt to each player, the only valid combinations are those of five cards.

Poker is of French-American origin and is the national vying game of the United States, though it has come to have a world-wide following in many different forms.

Orthodox Poker, cards arrange from highest to lowest:
Straight flush (five cards in suit and sequence, Ace high or low, as AKQJ10 or 5432A)
Fours (four cards of the same rank and one idler, as K-K-K-K-x)
Full house (three of one rank and two of another, as Q-Q-Q-4-4)
Flush (five cards in suit but not in sequence, as J-9-8-7-3)
Straight (five cards in sequence but not in suit, as 10-9-8-7-6)
Three of a kind, i.e. Threes, Triplet, or Trips (three of the same rank plus two of two different ranks, as 7-7-7-x-y)
Two pair (as Q-Q-9-9-x)
One pair (as 3-3-x-y-z)
High card (no combination: as between two such hands the one with the highest card wins)

Any game based on these five-card combinations in hands is a form of Poker, and any game lacking either or both of them is not poker, even if it has Poker as part of its title.