A central bank regulation requiring commercial banks to hold a minimum percentage of customer deposits as reserves, either as cash in their vaults or as deposits with the central bank, to ensure liquidity and stability in the banking system.

Reserve Requirements refers to the Federal Reserve's Regulation D framework governing reserve requirement ratios for depository institutions. As of March 26, 2020, the Federal Reserve reduced all reserve requirement ratios to zero percent, eliminating reserve requirements for all depository institutions.