An ace-high straight flush, commonly known as a royal flush, is the best possible poker hand in many variants of poker.
In poker, players form sets of five playing cards, called hands, according to the rules of the game. Each hand has a rank, which is compared against the ranks of other hands participating in the showdown to decide who wins the pot. In high games, like Texas hold ’em and seven-card stud, the highest-ranking hands win. In low games, like razz, the lowest-ranking hands win. In high-low split games, both the highest-ranking and lowest-ranking hands win, though different rules are used to rank the high and low hands.
Each hand belongs to a category determined by the patterns formed by its cards. A hand in a higher-ranking category always ranks higher than a hand in a lower-ranking category.
A hand is ranked within its category using the ranks of its cards. Individual cards are ranked, from highest to lowest: A, K, Q, J, 10, 9, 8, 7, 6, 5, 4, 3 and 2.
However, aces have the lowest rank under ace-to-five low or ace-to-six low rules, or under high rules as part of a five-high straight or straight flush. Suits are not ranked, so hands that differ by suit alone are of equal rank.
There are nine categories of hand when using a standard 52-card deck, except under ace-to-five low rules where straights, flushes and straight flushes are not recognized. An additional category, five of a kind, exists when using one or more wild cards.