Usually meaning the end of something, or a final part in something; that's the end.
Taken from the movie, Goodfellas during the scene where Tommy DeVito is supposed to be made a member of the Mafia.

*group enters an empty room*

Tommy DeVito: Aww no!

*Mob hitman shoots Tommy in the back of the head*

Mob hitman #1: And that's that.

Mob hitman #2: No fucking joke.

Mob hitman #1: Let's go, I'm fucking hungry.
by HatefulPilot September 02, 2011
Get a That's that mug for your bunkmate Sarah.