M1 is a category of the money supply that includes all physical currency and coin, demand deposits, traveler's checks, and other checkable deposits. It represents the most liquid forms of money that are readily available for spending.
The physical bills and coins in circulation within an economy.
Demand Deposit: Bank accounts from which deposited funds can be withdrawn at any time without any advance notice to the institution.
Liquid Assets: Assets that can be converted to cash quickly and without a loss in value