The FTSE 100, or Financial Times Stock Exchange 100 Index, tracks the performance of the 100 largest companies listed on the London Stock Exchange by market capitalization. Launched in 1984, it serves as the primary benchmark for the UK stock market and includes multinational corporations across sectors such as energy, finance, consumer goods, and mining. Investors and analysts use the FTSE 100 to gauge the health of the UK equity market and broader economic trends.