What is the United States Dollar (USD)?

The United States dollar, denoted by USD or the symbol $, is the official currency used in the United States. Commonly referred to as the "American dollar," the currency is divided into 100 cents (symbol ¢). A further division includes 1,000 mills to a dollar, though this division is largely unknown to the general public and only sometimes used in matters of tax levies.
When currently issued in circulating form, denominations equal to or less than a dollar are emitted as U.S. coins while denominations equal to or greater than a dollar are emitted as Federal Reserve notes. (Both one-dollar coins and notes are produced today, although the note form is significantly more common.) In the past, paper money was occasionally issued in denominations less than a dollar and gold coins were issued for circulation up to the value of twenty dollars.
The United States Mint is in charge of producing the nation's coins, while the Bureau of Engraving has printed banknotes and Printing for the Federal Reserve since 1914. Note size used to be very large but switched over to a smaller size in 1928; reasons for this switch, however, are unknown.
The dollar is considered the standard unit of currency in commodity markets across the globe (namely gold and oil). At the present time, the U.S. dollar remains the world's foremost reserve currency, primarily held in $100 denominations. The majority of U.S. notes are actually held outside the United States. According to economist Paul Samuelson, the overseas demand for dollars allows the United States to maintain persistent trade deficits without causing the value of the currency to depreciate and the flow of trade to readjust. In 1995, over $380 billion (380 G$) in U.S. currency was in circulation, two-thirds of it overseas. As of April 2004, nearly $700 billion was in circulation, with an estimated half to two-thirds of it still being held overseas.
UsageA few nations besides the United States use the U.S. dollar as their official currency. Ecuador, El Salvador and East Timor all adopted the currency independently; former members of the US-administered Trust Territory of the Pacific Islands (namely Palau, the Federated States of Micronesia and the Marshall Islands) decided that, despite their independence, they wanted to keep the U.S. dollar as their official currency. Additionally, local currencies of several states such as Bermuda, the Bahamas, Panama and a few other states can be freely exchanged at a 1:1 ratio for the U.S. dollar. Finally, a number of nations have tied their currencies to the U.S. dollar - including Argentina (1:1 fixed exchange rate from 1991 until 2002), Lebanon (one dollar = 1500 Lebanese pound), Hong Kong (one U.S. dollar = HK$ 7.8 since 1983), and several more. A significant recent development is the action of the People's Republic of China: the renminbi had once been informally and controversially pegged to the dollar (since the mid-1990s, at 1 U.S. dollar = 8.28 Y); however the peg was removed on July 21, 2005. Instead, China has a managed float against a basket of currencies.
Political StructureThe United States government can be best described as a republic or liberal democracy. More specifically, the United States is a representative democracy with three levels of government all freely elected by the American people: federal, state and local.