 The overnight policy rate (OPR) is the interest rate at which a depository institution lends immediately available funds (balances within the central bank) to another depository institution overnight.The amount of money a bank has fluctuates daily based on its lending activities and its customers’ withdrawal and deposit activity, therefore the bank may experience a shortage or surplus of cash at the end of the business day.Those banks that experience a surplus often lend money overnight to banks that experience a shortage so the banking system remains stable and liquid.