The United States dollar (symbol: $; code: USD; also abbreviated US$ to distinguish it from other dollar-denominated currencies; referred to as the dollar, U.S. dollar, American dollar, or colloquially buck) is the official currency of the United States and several other countries. The Coinage Act of 1792 introduced the U.S. dollar at par with the Spanish silver dollar, divided it into 100 cents, and authorized the minting of coins denominated in dollars and cents. U.S. banknotes are issued in the form of Federal Reserve Notes, popularly called greenbacks due to their predominantly green color.
The monetary policy of the United States is conducted by the Federal Reserve System, which acts as the nation's central bank.
The U.S. dollar was originally defined under a bimetallic standard of 371.25 grains (24.057 g) (0.7735 troy ounces) fine silver or, from 1837, 23.22 grains (1.505 g) fine gold, or $20.67 per troy ounce.