Collectible coins, particularly those issued by the United States, often include commemorative pieces, proof sets, and various denominations, including the 25-cent coin (quarter). Proof sets, such as those from 2015, are specially minted coins characterized by their high-quality finish and distinct mirror-like surfaces. These sets typically include coins that have not been released into circulation, making them desirable for collectors and investors. The 2015 Proof Set showcases various designs that represent both historical elements and modern artistry in American coinage.