Various denominations of currency, one form of money. Money is any token or other object that functions as a medium of exchange that is socially and legally accepted in payment for goods and services and in settlement of debts. Money also serves as a standard of value for measuring the relative worth of different goods and services and as a store of value. Some authors explicitly require money to be a standard of deferred payment.[1] Money includes both currency, particularly the many circulating currencies with legal tender status, and various forms of financial deposit accounts, such as demand deposits, savings accounts, and certificates of deposit. In modern economies, currency is the smallest component of the money supply. Money is not the same as real value, the latter being the basic element in economics. Money is central to the study of economics and forms its most cogent link to finance. The absence of money causes an economy to be inefficient because it requires a coincidence of wants between traders, and an agreement that these needs are of equal value, before a barter exchange can occur. The efficiency gains through the use of money are thought to encourage trade and the division of labour, in turn increasing productivity and wealth.