A coin is a unit of currency which has the approximate value of the metal it contains. Coins of copper or bronze have less value than those of silver or gold.
Generally a coin is stamped with the face of a nation's ruler, while the reverse has some official insignia.
Coins are often used to decide who goes first in games like American football. The front of a coin is called "heads" and the reverse "tails" when flipping a coin.