What's a MacGuffin?
It's a key plot element of probably every thriller ever made, and a lot of other movies, as well. It's the thing the characters want, and will do almost anything to obtain, and its most famous examples are always something ambiguous: the never-shown, glowing contents of the suitcase in Pulp Fiction (which may be a reference to the glowing contents of the suitcase in 1955's Kiss Me Deadly; the purposely vague mineral "Unobtanium" in Avatar; the secret plans in The 39 Steps; even the triforce from The Legend of Zelda. Alfred Hitchcock popularized the use of both the word and the technique, and describes it rather famously in a 1972 interview with Dick Cavett. Vimeo user Isaac Niemand created this cool animation to go along with the interview's audio, which is a really fun and succinct way to wrap your mind around what is inarguably a filmmaking fundamental.
McGuffin by Hitchcock from isaac niemand on Vimeo.