USD simply stands for United States Dollar, the currency of the United States. In a world of many different currencies and symbols, the simple USD acronym is easily understood by currency traders.
The dollar symbol, $, is also the symbol for the peso. The peso is the name of the currency for many Latin American countries. In Argentina, if you see a price of $10.00, the object costs 10 argentine pesos not 10 dollars.
Other countries also use the term dollar for their currency. Some dollar countries are Australia, Canada, Hong Kong and New Zealand. The value of a dollar in these countries with not be the same as a USD.
Currency traders use three letter indentifiers for all currencies. Euros are EUR and Japanese yen are JPY.
The currency trader and international traveler need to understand the difference between dollars, euros, pesos, reals and florints. The acronym USD makes it easy to find exchange rates.