MacGuffin

A MacGuffin is an object, device or goal that drives a story's plot and motivates its characters while remaining unimportant in itself, its exact nature often left unexplained or eventually revealed to be almost beside the point. The term was originated by the screenwriter Angus MacPhail and adopted and popularized by Alfred Hitchcock, who described the device as actually nothing at all, using an invented anecdote about a nonexistent apparatus for trapping lions in the Scottish Highlands. Hitchcock's 1935 film The 39 Steps built its plot around a MacGuffin of stolen military secrets, and later examples include the briefcase in Pulp Fiction, whose contents motivate several characters but are never revealed.