A poker hand where you hold four cards of a straight, missing one in the middle. For example 4578 and 5789 are inside straight draws, whereas 6789 is an outside, or open-ended, straight draw.

The distinction is important because only cards of one rank will complete your straight. In the above examples, both the first and second hands need a 6. The last hand makes a straight on either a 5 or a 10. An inside straight is only half as likely to be made as an outside straight, and are often not worth playing. This fact inspired the famous bit of poker advise:
Never draw to an inside straight.

Also known as a gutshot or a belly buster.

Technically, inside straight draws also include A234 and JQKA, because while they aren't missing a card in the middle of the straight, they still can only be completed by one card.