Coin

A coin is a piece of hard material, usually metal and usually round in shape, used as a form of money.

Coins were first used in Lydia in prehistoric times. Until relatively recent times, a coin was simply a piece of valuable metal (often gold or silver) whose weight was guaranteed by a government or other authority, whose value depended on its having a known weight of valuable material. Now, however, coins derive value simply by virtue of being declared legal tender by a government. Usually, the value of such coins is guaranteed by being backed by that government's reserves.