MacGuffin
An example of a MacGuffin is Marsellus Wallace's briefcase in the movie Pulp Fiction. Getting the suitcase and giving it back to Marsellus Wallace is the reason why Wallace's hit men are willing to kill other people and risk their lives to keep it, but what is inside the briefcase is never shown or explained. According to the movie's writer and director Quentin Tarantino, he says that whatever is in the briefcase is whatever the audience wants it to be, because such knowledge of what is inside does not affect the story at all.