used to show that you are certain you will not change your decision about something

I'm not coming and that's final. 我已经决定了，我不会来的。

You need to do exactly as I've told you and that's final.

We offered him a good contract with a salary of £50,000. That's final - we will not be negotiating the terms any further.

If there's any more of this nonsense, I'm leaving, and that's final.

I'm not inviting them to the wedding and that's final.

See also: final adjective