USD stands for United States Dollar, that means the United States dollar, the American currency. The dollar is the official currency of the country, but is also used in various countries of the world, on free movement, and in particular as international reserves.
The ISO 4217 international code of 3 letters for the various currencies. The abbreviation USD refers to the U.S. dollar, written before the numeric value, to demonstrate that the amount is in dollars. The International Monetary Fund refers to the dollar with the symbol $, an abbreviation that is used outside of the United States.
The term dollar comes from thaler, which is short for Joachimsthaler, a former silver coin used and that led to what is called a dollar currently. The dollar has been one of the most widely used currency in the world, but currently regulates the euro in terms of importance. The variation of the dollar fluctuates according to the market, and can either be in low, and high.
The United States have both notes as currency, and any amount less than one dollar, currency is issued.
USD is also a brand of extreme sports, which factory skateboards and skates.