Collectible coins are specially minted coins that are produced for numismatic interest rather than general circulation. In the United States, the 25-cent coin, or quarter, is a popular denomination among collectors. Proof sets, such as the 2020 United States Mint Proof Set, contain specially finished coins, including the quarter, with a mirror-like surface and sharp details, intended for collectors. These sets often include various denominations and are sought after for their quality and limited mintage.