M2

M2 is a definition of the money supply that includes everything in M1, but also adds savings deposits, money market funds, and certificates of deposit.

Definition

According to Principles of Economics by Timothy Taylor (3rd edition),

M2. A definition of the money supply that includes everything in M1, but also adds savings deposits, money market funds, and certificates of deposit.

According to Macroeconomics by Mankiw (7th edition),

M2. Various measures of the stock of money, where larger numbers signify a broader definition of money.