If two friends are arguing over which movie to watch at a sleepover, but then find out the TV isn't working, the debate becomes a moot point — there's no way to watch the movie anyway, so the argument no longer matters.
The phrase moot point originated in old English law schools where students debated fictional cases for practice. Now, it describes any issue that is open to debate but lacking practical impact or relevance. For instance, discussing who would have won a past game if the weather had been different is a moot point — it can't be changed, and debating it doesn't affect the outcome.