A Proof Coin (or just Proof) is a condition of a coin where the coin does not have any damage. Coins in this quality have not been circulated, but have been cased instead.
Because a Proof does not show any wear, the coin should be able to reflect light in the quality of a mirror. The coin should also not have any oil prints or any odour from human skin, which may devalue the coin. Proof coins are held in the best protection possible and will bring high values in a decade or two- it may depend on the coins' rarity or year it was issued.