Definition of gutshot
A gutshot is a belly straight draw. The difference between a regular straight draw and a gutshot is that a 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 by both bouts, i.e. 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 take our example from above. With 45 out of 67x, you have 8 outs so, you will roughly complete your print 1 out of 3 times returned to the river. As for the gutshot, you will complete your draw one time out of 6. There are double gutshot's that will give you the same probabilities of improving your hand. For example, if you have 45 out of 268, you have a double gutshot. This could be thought of as a double straight draw with a hole in it. Here, all 3's will give you the straight down and all 7's will give you the straight up.