Money is anything that is generally accepted as payment for goods and services and repayment of debts. The main functions of money are distinguished as: a medium of exchange, a unit of account, a store of value, and occasionally, a standard of deferred payment.

Money originated as commodity money, then evolved to easier-to-transport representative money, in which a certificate stands for a fixed quantity of a commodity. However, nearly all contemporary money systems at the national level are fiat money systems. Fiat money is without value as a physical commodity, and derives its value by being declared by a government to be legal tender; that is, it must be accepted as a form of payment within the national boundaries of the country, for "all debts, public and private". By law, the refusal of a legal tender (offering) extinguishes the debt in the same way acceptance does.

The money supply of a country is usually held to consist of currency (banknotes and coins) and demand deposits or 'bank money' (the balance held in checking accounts and savings accounts). These demand deposits usually account for a much larger part of the money supply than currency. Bank money is intangible and exists only in the form of various bank records. Despite being intangible, bank money still performs the basic functions of money, as checks are generally accepted as a form of payment and as a means of transferring ownership of deposit money.