Federal Funds Rate
The interest rate banks charge each other for overnight lending.
The federal funds rate is the FOMC's primary monetary policy tool. It sets the overnight lending rate between depository institutions, which ripples through to all other borrowing costs in the economy.
Rates at or near zero (0–1%) represent highly accommodative policy, designed to stimulate borrowing and investment. Rates above 5% are considered restrictive — borrowing costs rise, credit tightens, and business investment slows. The Fed historically raises rates to fight inflation and cuts them to fight recession.
The "real" fed funds rate (nominal rate minus inflation) is often more meaningful than the headline number. A 5% rate with 6% inflation is still negative in real terms — actually accommodative despite the high nominal level.