Coined by Alfred Hitchcock, a MacGuffin (sometimes McGuffin or maguffin) is "a plot element that catches the viewers' attention or drives the plot of a work of fiction". The defining aspect of a MacGuffin is that the major players in the story are (at least initially) willing to do and sacrifice almost 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, or a potential threat, or it may simply be something entirely unexplained.

The MacGuffin is common in films, especially thrillers. Usually, though not always, the MacGuffin is the central focus of the film in the first act, and then declines in importance as the struggles and motivations of characters play out. It may come back into play at the climax of the story, but sometimes the MacGuffin is actually forgotten by the end of the film. Multiple MacGuffins are sometimes—somewhat derisively—referred to as plot coupons.

(from wikipedia, the free encyclopedia)