An index of the 100 largest companies (by value) whose shares are traded on the UK stock market and which any member of the public can buy.
The FTSE 100 is calculated once a minute during trading hours. It covers the 100 largest companies by market capitalization. Changes to constituents are made once a quarter, according to a narrowly defined formula.
The FTSE 100 is a benchmark index tracking the performance of the London Stock Exchange. The full name is Financial Times Stock Exchange 100, but it's commonly called the Footsie. The FTSE 100 comprises the 100 largest companies traded on the exchange.