A MacGuffin is a plot element or other device used to catch the audience’s attention and maintain suspense, but whose exact nature has fairly little influence over the storyline.
“The main thing I’ve learned over the years is that the MacGuffin is nothing. I’m convinced of this, but I find it very difficult to prove it to others.” – Alfred Hitchcock
MacGuffin (a.k.a. McGuffin or maguffin) is a term for a motivating element in a story that is used to drive the plot. It serves no further purpose. It won’t pop up again later, it won’t explain the ending, it won’t do anything except possibly distract you while you try to figure out its significance. In some cases, it won’t even be shown. It is usually a mysterious package/artifact/superweapon that everyone in the story is chasing. To determine if a thing is a MacGuffin:
A. Check to see if it is interchangeable. For example, in a caper story the MacGuffin could be either the Mona Lisa or the Hope diamond, it makes no difference which. The rest of the story (i.e. it being stolen) would be exactly the same.
B. Does it do anything, and if it does, is it ever actually used in story? If the answer to both is yes, it’s a Plot Device, not a MacGuffin.
– Courtesy of tvtropes.org