Narrative
MacGuffin
An object, device, or event that is necessary to the plot and the motivation of the characters, but itself is insignificant.
In Depth
The audience doesn't care about the object itself; they care about what the characters will do to get it. It drives the plot but has little intrinsic value.
Example
"The briefcase in 'Pulp Fiction'. We never see what's inside, but it drives the entire story."