末了 is a colloquial noun meaning 'the end' or 'the final part' of something — a period of time, an event, or a story. It often appears in the adverbial phrase 末了 ('finally, in the end'), which is common in spoken Chinese. Unlike the near-synonym 最后, 末了 carries a slightly more casual, storytelling tone, as if you're wrapping up a narration. It is a noun, so it can follow 在 ('at the end') or be used as a standalone adverbial.