The term "proof", in conjuncion with coinage, is widely misunderstood. A proof coin is different than a "mint" coin because it is created especialy for collectors. The coin is pressed with the dye twice, as opposed to the standard single press. These coins are supposed to be flawless examples of the their specific coin type when they leave the mint, so many scratched or otherwise damaged proof coins are sent back into the mint to be melted down.