MacGuffin

A MacGuffin (sometimes McGuffin) is a plot device that motivates the characters or advances the story, but the details of which are of little or no importance otherwise. The element that distinguishes a MacGuffin from other types of plot devices is that it is not important what the object specifically is. Anything that serves as a motivation will do. The MacGuffin might even be ambiguous. Its importance is accepted by the story's characters, but it does not actually have any effect on the story. It can be generic or left open to interpretation. The MacGuffin is common in film, especially thriller. Commonly, though not always, the MacGuffin is the central focus of the film in the first act, and later declines in importance as the struggles and motivations of characters play out. Sometimes the MacGuffin is all but forgotten by the end of the film. According to film historian Kalton C. Lahue in his book Bound and Gagged (a history of silent-film serials), the actress Pearl White used... full article at wikipedia