Collectible coins, often referred to as numismatic coins, encompass a variety of types, including historical coins, commemorative issues, bullion coins, and rare varieties. In the United States, coins such as the Lincoln penny, Buffalo nickel, and Washington quarter hold significant value for collectors due to their historical significance and rarity. Collector interest often drives the market for these coins, influencing their prices based on factors like condition, demand, and mintage. The grading system is essential in determining a coin's quality and value, with established grading scales like the Sheldon scale used to evaluate numismatic quality.