The London interbank offered rate (Libor) and is the rate of interest at which banks in London are willing to lend to other banks.
Banking in London takes place in a huge range of currencies and Libor rates are available for many of them. Libor is often used as a benchmark to fix floating interest rates.
The Libor rate used as a benchmark is that calculated by the British Bankers Association (BBA). A number of banks report their rates to the BBA and a number based on these is released to the market daily.
Historical BBA Libor rates are published on the BBA Libor, and thre month rates are available daily on Twitter.