This seems the best answer

It seems like the best fit, but I'm not actually sure if that would apply either. The definition listed there is when a character talks directly to the audience, like in a Deadpool movie when he makes a joke as an aside, it seems to more apply to characters inside the story, not outside. I guess you can argue that the Narrator is considered a character in a story, but in my mind they've always seemed sort of nebulous and outside "the story" (with some exceptions to this). The Narrator is sort of always talking to the reader in a way (unless it's a character specifically narrating the events to another character).

I think that might be too broad for what OP is asking, though I don't know the answer. Their example has the narrator directly addressing the audience in a manner that acknowledges the existence of a reader for them to be addressing. Specifically they refer to a "you" which would be the reader. It's a bit like the term "4th wall breaking" in cinema although not quite the same as that either. Just "narration" means an entity, be it a character, or the author, or voice of God is telling the story and as it says in your link, is something present in all written literary works, but they won't necessarily acknowledge their audience, which is the unique characteristic they're trying to identify.

While that's also what I'd call it, it's a bit of a misnomer. The fourth wall is an acting term that refers to actors not interacting beyond the invisible wall that separates them from the audience. There isn't really any such rule that says an author can't address their readers directly in that way.

So I guess "The Monster At The End of This Book" would be 2nd person?

YOU CAN DO IT ATREU

I would think “aside” would be a better term.

Another commenter mentioned it.