Circulating Coins: Struck only once, no special handling or polishing. Uncirculated Coins: Struck like circulating coins, but with some quality enhancements, such as higher coining force or special packaging. Bullion Coins: Struck like circulating coins, but with a focus on precious metal content rather than collectibility. Reverse Proof Coins: Struck with a reverse proof finish, which has a different design finish and multiple polishes. Proof coins generally have a higher value than circulating coins due to their limited mintage, special handling, and high-quality finish. They are often sought after by collectors and can be sold at a premium price. In summary, proof coins are high-quality coins that have been specially treated and handled during the minting process, resulting in a unique appearance and higher value.