What is the meaning of "That's the stuff"?

[Omega]

English Language Tests, Intermediate level

ESL/EFL Test #54 "Lots of Stuff", question 8

......... the stuff! I want to hear it loud and clear and as much of it as you can manage. Well done!

(a) Here
(b) There
(c) That's
(d) More

English Language Tests, Intermediate level

ESL/EFL Test #54 "Lots of Stuff", answer 8

That's the stuff! I want to hear it loud and clear and as much of it as you can manage. Well done!

Correct answer: (c) That's

Your answer was: incorrect
Here the stuff! I want to hear it loud and clear and as much of it as you can manage. Well done!
_________________________

What is the meaning of "That's the stuff"?

Omega

[Mister Micawber]

.
That's a good, vigorous effort!
.
_________________
Native English teacher at Mister Micawber's