Money supply
In macroeconomics, money supply ("monetary aggregates", "money stock") is the quantity of currency and checkable deposits in the hands of the non-bank public available within the economy to purchase goods, services, and securities. The money supply affects the interest rates. The two are related inversely, such that, as money supply increases interest rates will fall. When the interest rate equates the quantity of money demanded with the quantity of money supply, the economy is working at the money market equilibrium.

The money demand market uses the same tools of analysis as to other markets: supply and demand result in an equilibrium price, where the free market (or long term) interest rate plus the quantity of real money available balances the demand for money. Short term rates are artificially manipulated by the Federal Reserve in the open market.
When thinking about the "supply" of money, it is natural to think of the total of banknotes and coins in an economy. That, however, is vastly incomplete. In the United States, coins are minted by the United States Mint, part of the Department of the Treasury, outside of the Federal Reserve. Banknotes are printed by the Bureau of Engraving & Printing on behalf of the Federal Reserve System. The Federal Reserve can also create book-keeping credits in the reserve accounts of its member banks, on the same terms as it can issue paper banknotes (by pledging collateral, usually in the form of US Treasury securities). As it always stands ready to exchange these book-keeping credits for paper banknotes, they are functionally equivalent.
In this respect, all paper banknotes in existence are systematically linked to the expansion of the electronic, credit-based money supply. Coinage can be increased or decreased outside this system by Legal Mandate or Legislative Acts. However, at present the coin base is held in check and used as a complementary system rather than a competitive system with private bank issue of electronic, credit-based money. The common practice is to include printed and minted money supply in the same metric M0.
The more accurate starting point for the concept of money supply is the total of all electronic, credit-based deposit balances in bank (and other financial) accounts (for more precise definitions, see below) plus all the minted coins and printed paper. The M1 money supply is M0, plus the total of (non-paper or coin) deposit balances without any withdrawal restrictions (restricted accounts that you can't write checks on are put in the next level of liquidity, M2).
The relationship between the M0 and M1 money supplies is the money multiplier — basically, the ratio of cash and coin in people's wallets and bank vaults and ATMs to Total balances in their financial accounts. The gap and lag between the two (M0 and M1 - M0) occurs because of the system of fractional reserve banking.