MacGuffin

A MacGuffin is a plot element that catches the viewers attention or drives the plot of a work of fiction. The aspect of a MacGuffin is that the major players in the story are willing to do and sacrifice anything to obtain it, regardless of what the MacGuffin actually is. In fact, the specific nature of the MacGuffin may be ambiguous, undefined, generic, left open to interpretation or otherwise completely unimportant to the plot. Common examples are money, victory, glory, survival, a source of power, a potential threat, or it may simply be something entirely unexplained.

'We have a name in the studio and we call it 'MaGuffin' it is the mechanical element that usually crops up in any story. In crook stories it is always the necklace and in spy stories its always the papers.' - Alfred Hitchcock