A youtube video that inevitably leads to a youtube trance or a youtube trip. A youtube trap consumes large chunks of time and is usually triggered in the midst of doing something important i.e. project, assignment, or generally studying.
Dave: "I was studying for my final tomorrow when Mike sent me a youtube video with a funny kitten in a cup, 2 hours later I'm watching 2 girl 1 cup reaction videos."
Taylor: "Lol he sent you a youtube trap."