Since this is lifted from TV Tropes, I'll just quote:
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 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. In some cases, it won't even be shown. It is usually a mysterious package/artifact/superweapon that everyone in the story is chasing.
For our purposes, the MacGuffins in question might actually end up being important to the plot, but not because they are actually important, but because the plot is so stupid that it required chasing after something completely pointless for no other reason than that the script required it.
Examples
- Eternal Darkness: The holy artifact Pious Augustus is chasing after is both a MacGuffin and a giant buttplug.
- Final Fantasy X-2: The AWESOM-O Sphere is wanted by everyone for reasons no one can quantify, and ends up being a piece of shit. Too bad, since it's one of the few spheres the Gullwings actually find.
- Grandia II: The Granaschlong.
- Legend of Zelda: Ocarina of Time: To be clear, the Spiritual Stones DO have a purpose--to open the Door of Time and allow entrance to the Sacred Realm. It's just that that is a really fucking bad idea, and Twink and Zelda should have just left them alone. But they didn't, because they're stupid.
- Xenosaga Episode I: There are a lot of them. In fairness, the collective Miltia MacGuffins do serve a purpose in the larger series, but taking Xenosaga as a standalone game, everyone is chasing them because they do Stuff and they're supposed to.
- Xenosaga Episode II: So, remember the MacGuffin Data from the first game that was totally important and made MOMO important because she alone possessed it? Not only does that continue being a MacGuffin, but Canaan also had the same data the entire time and nobody brought it up.