Coin set

A coin set, or mint set, is a collection of uncirculated or proof coins, released by a mint.

[1] Occasionally the coins for annual mint sets are struck with special coin dies.

"[2] Early coin sets were issued in paper or cardboard folders which often led to toning, due to the sulphur content of the card.

Collectors post images on their web site.

They are valued by collectors because they are needed to complete coin sets.