Collectible coins, such as the 2010 Proof Sets from the United States, are specially produced coins that feature a mirror-like finish and are made for collectors. Each set typically includes coins from that year, including the 25-cent (quarter) coins, often showcasing different designs representing each state or national park. Proof coins are struck using polished dies and are made in limited quantities, enhancing their appeal and value among numismatists. These sets serve as a way for collectors to obtain high-quality versions of circulating coins.