Most often used to refer to a draw requiring multiple cards, such as a draw on the flop needing both the turn and river cards to be completed. For example, in hold’em, someone holding {A-Diamonds}{7-Diamonds} on a {K-Diamonds}{9-Clubs}{2-Spades} flop has a backdoor flush draw, needing two more diamonds to make a “backdoor flush.” A player holding {K-Diamonds}{J-Clubs} on a {Q-Clubs}{7-Spades}{4-Hearts} flop has a backdoor straight draw, needing a run out of either {A-}{10-} or {10-}{9-} to make a “backdoor straight.”

The term is also occasionally used to refer to any made hand that wasn’t necessarily the player's original hope for a hand. For example, the player holding {A-Diamonds}{7-Diamonds} on that {K-Diamonds}{9-Clubs}{2-Spades} flop then watches two sevens come on the turn and river, thus giving him “backdoor trips.”