A coin is a small, flat, round piece of metal or plastic used primarily as a medium of exchange or legal tender. They are standardized in weight, and produced in large quantities at a mint in order to facilitate trade. They are most often issued by a government. Coins often have images, numerals, or text on them. Obverse and its opposite, reverse, refer to the two flat faces of coins and medals. In this usage, obverse means the front face of the object and reverse means the back face. The obverse of a coin is commonly called heads, because it often depicts the head of a prominent person, and the reverse tails.
Coins are usually metal or an alloy, or sometimes made of manmade materials. They are usually disc shaped. Coins made of valuable metal are stored in large quantities as bullion coins. Other coins are used as money in everyday transactions, circulating alongside banknotes. Usually the highest value coin in circulation is worth less than the lowest-value note. In the last hundred years, the face value of circulation coins has occasionally been lower than the value of the metal they contain, for example due to inflation.