Definition
A McGuffin (also spelled 'MacGuffin') is a plot device in a film or story that motivates the characters and drives the plot forward, but is ultimately unimportant in itself. It's something the characters care about, but the audience doesn't need to. Think of it as a red herring or a distraction. The specific nature of the McGuffin is irrelevant; its purpose is to get the characters moving and interacting. The term was popularized by Alfred Hitchcock.