It might be a Scottish name, taken from a story about two men on a train. One man says, “What’s that package up there in the baggage rack?” And the other answers, “Oh, that’s a MacGuffin”. The first one asks, “What’s a MacGuffin?” “Well,” the other man says, “it’s an apparatus for trapping lions in the Scottish Highlands.” The first man says, “But there are no lions in the Scottish Highlands,” and the other one answers, “Well then, that’s no MacGuffin!” So you see that a MacGuffin is actually nothing at all.
Alfred Hitchcock popularized but did not invent the MacGuffin. The plot device predates its term. A MacGuffin is an object or element in a narrative that impels the characters to progress through the plot, while usually having very little or value in and of itself. The MacGuffin seems relevant, but its actual worth is often negligible. Like the titular Maltese Falcon. Like Rosebud in Citizen Kane. They motivate change but they do not offer any outcome.
This device may translate well to the sort of performance-driven ‘game’ I’m trying to coax into workable form. For players to interact in any meaningful dramatic form, some relevant, or seemingly relevant motivator is required. Any playthrough of any game might have been dramatically interesting if this weren’t the case. Assuming for now that it isn’t, the MacGuffin might be a mountain in the distance. It might be a crumbling bridge. More relevantly, it was the boat in the distance in my own game, Raft. You were never meant to reach the boat, but it impelled-first time players to use their performance controls, like panicked waving. And thereby laid the ground rules for inter-player performance.

It seems like, at least until testing proves otherwise, that this sort of approach is warranted to transport players from objective-minded play to dramatic-minded play. That is the assumption, for now, at least.
Tenet: A game-related MacGuffin Objective is necessary to induce players into a dramatic performance.