MacGuffin.

Definition of a MacGuffin.

A MacGuffin is a plot device that has no specific meaning or purpose other than to advance the story; any situation that motivates the action of a film either artificially or substantively. Orginally coined by Alfred Hitchcock where it was used in a story set on a Scottish train. A modern example of a Macguffin is the suitcase case in Pulp Fiction, we never know what the insides of the suit case actually is but only the reaction people give as they open it up, a light beam comes out of the suit case aswell maybe showing that it's something beautiful, thats why the people who look within the suit case give such a shocked and pleased reaction.