“[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 almost always the necklace and in spy stories it is most always the papers … It might be a Scottish name, taken from a story about two men in a train. One man says, ‘What’s that package up there in the baggage rack?’ And the other answers, ‘Oh that’s a MacGuffin.’ The first one asks, ‘What’s a MacGuffin?’ ‘Well,’ the other man says, ‘It’s an apparatus for trapping lions in the Scottish Highlands.’ The first man says, ‘But there are no lions in the Scottish Highlands,’ and the other one answers ‘Well, then that’s no MacGuffin!’ So you see, a MacGuffin is nothing at all.”

— Hitchcock on MacGuffins via - io9