A MacGuffin is an object, event, or person that the characters in a story value greatly. Almost the whole plot revolves around it, even though the thing itself isn’t actually important to the unfolding story. The most common type of MacGuffin is a person, place, or thing, such as money or an object of value.
Think of the falcon in
the Maltese Falcon movie. The black falcon statuette, called the
“Maltese Falcon” is the MacGuffin in the movie and the plot
revolves around ownership and finding it. The Rabbit's Foot in
Mission: Impossible III is a modern MacGuffin.
Scenario editor Angus
MacPhail established the term MacGuffin for the unknown plot
objective which you did not need to choose until the story
planning was complete. Some say it comes from the word guff,
which is defined as meaning nonsense and MacPhail added Mac from
his name to the front of it. Alfred Hitchcock adopted and used
the word to the end of his career.