Reserve requirement
The reserve requirement (or cash reserve ratio) is a central bank regulation that sets the minimum amount of reserves that must be held by a commercial bank. The minimum reserve is generally determined by the central bank to be no less than a specified percentage of the amount of deposit liabilities the commercial bank owes to its customers. The commercial bank's reserves normally consist of cash owned by the bank and stored physically in the bank vault (vault cash), plus the amount of the commercial bank's balance in that bank's account with the central bank.
The required reserve ratio is sometimes used as a tool in monetary policy, influencing the country's borrowing and interest rates by changing the amount of funds available for banks to make loans with.