A jump cut is when you are filming yourself or someone and as an example, your body is in one position and you turn off the cam, then move some, turn cam back on and start filming. It gives you the appearance of jumping or skipping. I see this sometimes when someone messes up on a line and they splice the first take (good part of the line) with a 2nd take (replacing the part they messed up on.) This is considered to be very unprofessional in the business because it just looks like a home video rather than a professional film. It sometimes happens in editing also when you may splice something together and your frames dont match up exactly.
I have seen this in a few videos and just wanted to mention it for those who may not think about it while filming or editing. If you mess up on a line the best thing to do in my opinion is reshoot it from the start of that scene. You should see some of the raw footage of my trying to say my lines and messing up 7 or 8 times in a row LOL. We should all do one big blooper real one day!!!