A backdoor straight is forming a straight by hitting community cards on turn and river when you had no straight draw on flop.
Explanation. For example, holding 7‑8, flop 9‑J‑2: no draw. But turn Q and river 10 complete straight. The term describes drawing “backdoor” by hitting two cards late. It’s rare but can swing pots unexpectedly and matters when evaluating speculative holdings or bluff lines.