Straight Draw

draws

Four cards that need one more to make a straight.

OESD = 8 outs (~32% by river). Gutshot = 4 outs (~16%). Double gutshot is also 8 outs but harder to spot.

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.
Flush Draw
Four cards of the same suit, needing one more for a flush.
Gutshot
An inside straight draw — needing one specific rank (4 outs).