The graph to the left is for the 3 month LIBOR.
LIBOR, or the London Interbank Offered Rate, is the average interest rate between banks in the London interbank market. LIBOR is a widely used short-term interest rate benchmark since it is designed to reflect the cost of borrowing between some of the world's largest, most reputable banks.
There isn't just one LIBOR; there are numerous rates determined by two variables:
Every business day at just after 11:00 am London time, the British Bankers' Association, in conjunction with Reuters, releases new rates for each combination of these. For example, there's a new 3-month LIBOR for the yen, overnight LIBOR for the euro, and 2-week LIBOR for the pound released daily. These rates indicate both the health of the currencies (and their respective economies) relative to one another and expectations about future economic conditions.
There are ten LIBOR panels, one for each of the ten currencies for which the rate is determined. Each panel is composed of at least eight contributor banks, chosen for their reputations and their perceived expertise in a given currency. The BBA takes the daily deposit rates reported by its designated contributor banks and calculates the mean of the middle 50%; the resulting number is the LIBOR for the currency in question. The average rates at which these banks say they would lend to one another is taken as an indication of the health of the banking systems of the ten LIBOR currencies. A list of the panels and their members as of May 30, 2008, can be found here on the British Bankers' Association's website.
Not only does LIBOR provide information about the cost of borrowing in different currencies, it actually influences it. LIBOR is used as the basis for other interest rates across the globe. IE, variable interest rate loans such as mortgages and car loans will often be quotes at LIBOR + a percentage. For example, a loan that was LIBOR + 5% would charge 10% interest when the LIBOR is 5%, and 7% when the LIBOR is 2%.
LIBOR impacts financial instruments and products including:
On May 29, 2008, the Wall Street Journal reported that certain banks had been reporting lower rates to the BBA than what WSJ analysis suggested they should have been. Given the trillions of dollars tied to the LIBOR, even a small inaccuracy in either direction can cost lenders, borrowers, companies, or even whole economies billions of dollars. The WSJ study estimated that, if true, the artificially low U.S. dollar LIBOR saved U.S. borrowers about $45 billion over the first four months of 2008. The banks, however, denied this claim and stuck by the rates they'd reported to the BBA and Reuters.