Flush Draw

draws

Four cards of the same suit, needing one more for a flush.

Flush draws have ~36% equity from flop to river vs one pair. Combined draws (flush + straight, flush + pair) can have 60%+.

See also

Backdoor
A draw needing two perfect cards (turn + river) to complete.
Drawing Dead
Having no card left in the deck that can win the hand.
Gutshot
An inside straight draw — needing one specific rank (4 outs).
OESD
A straight draw with two ranks completing it (8 outs).