That-s-it Definition

phrase

Finished. There is nothing more to the issue. That's all.

So, that's it? I thought there would be some more.

Wiktionary

Lewis Carroll, Alice's Adventures in Wonderland, Chapter 7:A bright idea came into Alice’s head. “Is that the reason so many tea-things are put out here?” she asked.“Yes, that’s it,” said the Hatter with a sigh: “it’s always tea-time, and we’ve no time to wash the things between whiles.”

Wiktionary