Covers & Covers of Covers

Will someone please tell me what the musical technique in these clips is called? I'm sure there's a better way to describe it than "editing one or two people performing/playing multiple parts into a single track". I'm too lazy to figure it out. I'm also too lazy to continue framing for the new bathroom subfloor right now, so I'm going to sit here for several minutes and wait for the interwebz to bring me the answer.