The interbank money market is a market in which banks extend loans to one another for a specified term. Most interbank loans are for maturities of one week or less, the majority being overnight. Such loans are made at the interbank rate (also called the overnight rate, if the term of the loan is overnight).
Banks are required to hold an adequate amount of liquid assets, such as cash, to manage any potential bank runs by clients. If a bank cannot meet these liquidity requirements, it will need to borrow money in the interbank market to cover the shortfall. Some banks, on the other hand, have excess liquid assets above and beyond the liquidity requirements. These banks will lend money in the interbank market, receiving interest on the assets.
The interbank rate is the rate of interest charged on short-term loans between banks. Banks borrow and lend money in the interbank lending market in order to manage liquidity and satisfy regulations such as reserve requirements.
The interest rate charged depends on the availability of money in the market, on prevailing rates and on the specific terms of the contract, such as term length.