McGuffin (aka: MacGuffin or maguffin) is a term for a plot enabling device, i.e. a device or plot element in a movie that is deliberately placed to catch the viewer’s attention and/or drive the logic of the plot, but which actually serves no further purpose - it won’t pop up again later, it won’t explain the ending, it won’t actually do anything except possibly distract you while you try to figure out its significance. More specifically, it is usually a mysterious package or superweapon or something that everyone in the story is chasing.
Possibly coined by Alfred Hitchcock. The perfect example is the “government secrets” that motivate the action in “North By Northwest” (1959). Another typical McGuffin is the Maltese Falcon. It gets the characters together, pits them against each other, but turns out to be worthless.
Also used by Quentin Tarantino in “Pulp Fiction” in the form of the suitcase with the mysterious glowing contents.