What is a proof coin?

Business English Lesson, Advanced Level

ESL/EFL Test #180 [color=blue]“The US Mint”, question 9

It also produces proof and uncirculated coins, coins, and medals for sale to the general public.

(a) commemorative
(b) commissioned
(c) memento
(d) memorabilia

Business English Lesson, Advanced Level

ESL/EFL Test #180 [color=blue]“The US Mint”, answer 9

It also produces proof and uncirculated coins, commemorative coins, and medals for sale to the general public.

Correct answer: (a) commemorative
[size=200]_________________________[/size]

What does proof mean here?
thanks.

A proof coin is an uncirculated coin that has been made especially carefully. They are sold to collectors or issued as memorabilia.