0 something in a film that moves the plot (= story) forward but is not important itself:
Most mysteries have a MacGuffin, an event or item designed to motivate the characters but which is actually just a meaningless placeholder.
Hitchcock described the "MacGuffin" as a meaningless, unimportant detail that solely existed to serve as a reason for the story to exist.
A MacGuffin is something that an entire story is built around and yet has no real relevance.
The pregnancy is kind of a MacGuffin: it motivates her to realize her feelings for the man who fathered the child.
The characters' literary obsession is ultimately a MacGuffin, since it's not what they do as a profession, but what they do with their lives, that the film is interested in.
A MacGuffin's importance is usually debunked or forgotten as the story unfolds.
