What is a "Jump cut?" Answer: A hard cut transition from one scene to another where both scenes are from the same shot (and camera angle). These can be disorienting for the viewer because they break the natural flow of time and space.
This type of edit causes the subject of the shots to appear to "jump" position in a discontinuous way. For this reason, jump cuts are considered a violation of classical continuity editing, which aims to give the appearance of continuous time and space in the story by de-emphasizing editing.
Jump cuts, in contrast, draw attention to the constructed nature of the film. Although the term is sometimes used in a loose way, a cut between two different subjects is not a true jump cut, no matter how jarring.
Continuity editing uses a guideline called "the 30 degree rule" to avoid jump cuts. The 30 degree rule advises that for any consecutive shots, the camera position vary at least 30 degrees from the previous position. Generally, if the camera position changes 30 degrees or more, the spectator experiences the edit as a change in camera position rather than a jump in the position of the subject. Although jump cuts can be created through the editing together of two shots filmed non-continuously, they can also be created by removing a middle section of one continuously-filmed shot.
The jump cut can be used to make a point or direct the viewer to the subject, like jarring you into paying attention. But for the most part you should never use them. It's easy to push record, stop then start recording again and cause a jump cut. Your home movies are probably filled with them.
Whenever you press record on your camcorder you are telling a story, even if you didn't plan to. Your story will either have a start, middle and end or it will wander aimlessly. Jump cuts are a quick indicator of a planned or unplanned video. If you are shooting with the intention of in-camera editing then you will probably always want to avoid the jump cut. If you are shooting to edit then you can remove the jump cut later, provided you shot something or an angle to replace it. Usually a simple cut away will smooth over a jump cut.
So watch those jump cuts and keep your video flowing forward with seamless edits. Have fun and go shoot something!