The term “backdoor” in poker refers to a situation where a player needs both community cards (turn and river) to improve their hand. For example, if a player has two clubs in hand and the flop comes down another club, the player has a “backdoor” of clubs - they need clubs both on the turn and on the river to hit a flush.

As a result, a “backdoor” refers to the chance to improve your hand, but only if both community cards come up in your favor. This differs from an “open-ended” draw situation, where only one card is needed to complete the hand.