MacGuffin
Also said as Plot coupon, The thing everyone wants
An object that everyone in the story is chasing, whose actual nature hardly matters. Alfred Hitchcock made the word famous.
It gets characters moving and in each other's way without any explanation. If players start asking what it actually does, you have either a plot problem or a better story than you thought.
Say it
“The stone is a MacGuffin, so do not write a lore page for it. Spend those words on why these three people are willing to kill each other over it.”
Where you’ve seen it
Uncharted 2 sends everyone racing after the Cintamani Stone, and it matters mostly because the people with guns want it before Drake gets to it.
Not to be confused with chekhov's gun
Chekhov's gun has to do something when the time comes. A MacGuffin only has to be wanted.