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. Collectors often value rare coins for their potential to appreciate in value over time. The market for rare coins can be influenced by demand, condition, and provenance. Notable rare coins include the 1909-S V.D.B. Lincoln penny and the 1794 Flowing Hair dollar, both of which are famous among numismatists.