Currency is a medium of exchange for products and services. In short, it is money, in the form of coins and paper, usually issued by a government and generally accepted at its face value as a method of payment.
USD is the official currency of the United States of America. Current annual inflation rate is around 5%. The US dollar is managed by Federal Reserve in Washington, D.C., United States. The symbol of USA dollar is $.
EUR is the official currency of European Union. Currently the annual inflation rate is around 6.9%. Euro is managed by European Central Bank in Frankfurt, Germany, and Eurosystem. The symbol of Euro is €.