This means that I’ve sold enough copies that I’ve paid back my advance, and any royalties now come to me. This is exciting! Comeuppance is now The Little Story That Could in my mind.
This doesn’t mean the book hasn’t made a profit for the publisher until now. My royalties are a percentage of the hard copy’s or e-book’s profit. ( A different percentage for each format.) Many books are profitable and at least break even for the publisher without ever earning out the author’s advance.
We’ve all heard horror stories of advances being clawed back by the publisher, but those are mostly specific, and extreme, cases. And I won’t be one (at least this time) so, yaaay!