Hitchcock 'Maguffin'

A Macguffin (sometimes McGuffin or Maguffin) is ba plot device that motivates the characters and advances the story, but has little other relevance to the story.
'We have a name in the studio, and we call it the 'MacGuffin'. It is the mechanical element that usually crops up in any story. In crook stories it is always the neck and in spy stories it is always the papers.'