A measure of the amount of money in circulation. Various measures of money supply exist.
The broadest measure, M4, is the sum of money held in notes and coins, the total amount lent by banks, to individuals, companies and other banks, and the total amount of money borrowed by the government.
The narrowest measure, M0, is made up of notes and coins in circulation, the money in banks' tills and in the money they hold at the Bank of England.