Definition of 'M2'
A measure of money supply that includes cash and checking deposits (M1) as well as near money. “Near money" in M2 includes savings deposits, money market mutual funds and other time deposits, which are less liquid and not as suitable as exchange mediums but can be quickly converted into cash or checking deposits.
Investopedia explains 'M2'
M2 is a broader money classification than M1, because it includes assets that are highly liquid but not cash. A consumer or business typically won’t use savings deposits and other non-M1 components of M2 when making purchases or paying bills, but it could convert them to cash in relatively short order.
M1 and M2 are closely related, and economists like to include the more broadly defined definition for M2 when discussing the money supply, because modern economies often involve transfers between different account types. For example, a business may transfer $10,000 from a money market account to its checking account. This transfer would increase M1, which doesn’t include money market funds, while keeping M2 stable, since M2 contains money market accounts.