The United States dollar (symbol: $; code: USD; also abbreviated US$ or U.S. Dollar, 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 its territories.
The U.S. dollar was originally defined under a bimetallic standard of 371.25 grains (24.057 g) fine silver or, from 1837, 23.22 grains (1.505 g) fine gold, or $20.67 per troy ounce. The Gold Standard Act of 1900 linked the dollar solely to gold. From 1934 its equivalence to gold was revised to $35 per troy ounce. Since 1971 all links to gold have been repealed.
The U.S. dollar became an important international reserve currency after the First World War, and displaced the pound sterling as the world’s primary reserve currency by the Bretton Woods Agreement towards the end of the Second World War.