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2.
1. A discussion that is no longer up for debate. 2. A decision is made and there is no room for change or questioning.
The sky is blue and thats that.
by MJ and Akay February 23, 2010
 
1.
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