My third and final (for the moment) lazy-catch-up post:
A MacGuffin (sometimes McGuffin or Maguffin) is a plot device that motivates the characters and advances the story, but has little other relevance to the story.The director and producer Alfred Hitchcock popularized both the term "MacGuffin" and the technique. According to the Oxford English Dictionary, Hitchcock explained the term in a 1939 lecture at Columbia University: "[W]e 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 necklace and in spy stories it is always the papers."