Other forms: fidos
Fido may sound like a dog's name, but it's also a term for a rare, collectible coin with a mistake in its design. Coin collectors get excited when they come upon a fido (dog lovers do too).
Fido, coined in 1967 by coin experts, is an acronym of "freaks, irregulars, defects, and oddities." These coins, considered defective by the mints that produced them, are exciting prizes to numismatists, or coin collectors. Examples of valuable fidos include the "three-legged buffalo," a buffalo nickel that was minted with a missing leg in 1937 and is now worth over $100,000.