A more general definition is that a currency is a "system of money" (monetary units) in common use, especially for people in a nation. Under this definition, U.S. dollars (US$), euros (€), Japanese yen (¥), and pounds sterling (£) are examples of currencies. These various currencies are recognized as stores of value and are traded between nations in foreign exchange markets, which determine the relative values of the different currencies. Currencies in this sense are defined by governments, and each type has limited boundaries of acceptance.