Definition of gutshot
A gutshot is a belly flush draw. The difference between a regular straight draw and the gutshot is that the gutshot will give us 4 outs rather than 8 outs like a regular straight draw. If you have 45 out of 67x, you have a straight draw on both ends, meaning that you can be helped by 2 cards, the 3 and the 8. In the deck, there are theoretically four 3s and four 8s left for 8 outs. As for the gutshot, imagine that you still have 45, but on 26x. Here you have a gutshot because you absolutely need a 3 to complete your hand.
The gutshot will have less equity than a regular draw
Let's go back to our example above. With 45 out of 67x, you have 8 outs, so you will roughly complete your draw 1 out of 3 times on the river. As for the gutshot, you will complete your draw 1 out of 6 times. There are double gutshots that will give you the same odds of improving your hand. For example, if you have 45 out of 268, you have a double gutshot. You could think of it as a double gutshot. Here, all 3s will give you the straight down and all 7s will give you the straight up.