Money aggregates are broad categories that measure the money supply in an economy. In the United States, labels are attributed to standardized monetary aggregates:

MO Physical paper and coin currency in circulation, plus bank reserves held by the central bank also known as the monetary base

M1: All of M0, plus traveler's checks and demand deposits

M2: All of M1, money market shares, and savings deposits

A legacy aggregate known as M3, which further included time deposits over $100,000 and institutional funds, has not been tracked by the Federal Reserve since 2006 but is still calculated by some analysts.