A currency in the most specific sense is money in any form when in use or circulation as a medium of exchange, especially circulating banknotes and coins.
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 (€), Indian rupee (₹), Japanese yen (¥), and pounds sterling (£) are examples of currencies.
Currencies may act as stores of value and be 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.