Gutshot (inside straight draw)
Also called inside straight draw, belly buster
A gutshot (inside straight draw) is a hand needing one specific rank to fill a straight, leaving a single gap in the middle of four cards.
A gutshot, also called an inside straight draw, is when four of the cards you can use have a one-card hole in the middle of the sequence. Only one rank fills that gap, so you have just four cards in the deck that complete your straight. That makes it a thin draw compared to an open-ended straight draw, which can be filled from either end and has eight cards that help.
It comes up most often on the flop or turn. Say your two hole cards plus the board give you 5-6-7-9 with no 8 yet: any 8 makes your straight, and nothing else completes it. You'll hear players say they're drawing to the gut or that they caught their gutshot when that one card arrives.
For a beginner, the key thing is that a gutshot misses far more than it hits, so it's usually not worth chasing with big chips unless the price is cheap or you have extra ways to win. Folding a bare gutshot to a large bet is often fine. The math behind this lives in ideas like outs (you have four) and pot odds, and a gutshot gains value when it also picks up a flush draw or overcards, or when you can use it as a semi-bluff.
Example
You hold J-9 and the board comes 7-8-K rainbow: your best straight cards are 7-8-9-J, so only a 10 fills the middle to make 7-8-9-10-J. That lone-rank gap, with just four 10s to complete it, is the classic gutshot. (Contrast an open-ender like 7-8-9-10, where either a 6 or a J finishes the straight.)