Money Supply
Money supply is the measured stock of money — M0/MB, M1, M2 — a quantity that depends on what you count as money.
Definition
MB is reserves plus currency. M1 adds checkable deposits. M2 adds savings-like deposits and retail MMFs (definitions changed in 2020). Credit creation, not the printing press cartoon, is most of M2. Velocity is the fudge that makes MV=PY hold.
Why it matters
Monetarist stories and 2020–22 inflation debates used M2. The mapping to CPI is loose once velocity and composition move.
Case
US M2 surged in 2020–21 and then contracted YoY. Inflation rose and then cooled with a lag that invited every ideology.
How to read it
Which M, what changed in the definition, and whether the impulse is deposits or credit. Do not treat M2 as a policy instrument the Fed sets like the funds rate.