Rare coins are unique or limited-edition coins that are highly sought after by collectors and investors. Their rarity can be due to factors such as low mintage, historical significance, or unique features. Examples include coins from specific years, mint marks, or those with errors during production, which can greatly increase their value. Collectors often seek rare coins for their investment potential and historical importance. The value of a rare coin can fluctuate based on market demand, condition, and provenance. Organizations like the Professional Coin Grading Service (PCGS) help authenticate and grade these coins, ensuring buyers know their quality and worth.