A coin is a small, flat, (usually depending on the country or value) 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.