Open-ended refers to a situation in poker where the player has four of five cards needed for a straight that can be completed at either end.
This situation is also called an outside straight draw or double-ended straight draw as the cards needed to complete the straight are cards which are on the outside (both ends) of the current hand, as opposed to an inside draw such as 2♦ 3♠ 4♠ 6♥ or A♣ 2♣ 3♣ 4♦, which can only be completed by a five.
The term originated with draw poker but is also used in games like Texas hold'em.
But unlike simple inside draws, two ranks can fill the hand.
Such hands are optimal drawing hands, since the player has up to fifteen outs (nine cards remaining in the suit, six cards which complete the straight but not the flush).