A jump cut is a transition that creates a lack of continuity by leaving out parts of the action, and it also helps to give a sense of elipses in time. Its mostly used when the editor want to cut to a similar shot which are framed the same. These jump cuts can add tension impact in the right place where needed if used in the right way and place.
In this video example, it shows to objects in the frame, and after a few seconds it jumps to the same frame but with one of the objects missing and vice versa. This is an example of a jump cut in it simpliest form.