A royal flush is a poker hand containing an ace, king, queen, jack, and a 10 of the same suit (for example A♠ K♠ Q♠ J♠ 10♠). Because it is both a straight (having five cards in sequential rank) and a flush (having five cards of the same suit), it is also known as an ace-high straight flush.
A royal flush is not actually a separate type of hand in poker. It is ranked as a straight flush, but since it has an ace as the highest card, it is the highest ranking straight flush, and therefore the highest ranking hand in poker (sans wild cards).
The probability that a random five card hand is a royal flush is 1 in 649,740.
