The FTSE 100, or Financial Times Stock Exchange 100 Index, is a stock market index that represents the 100 largest companies listed on the London Stock Exchange. These companies are selected based on their market capitalization, which is the total value of their outstanding shares. The FTSE 100 is often used as a benchmark to gauge the performance of the UK stock market and the economy. Investors and analysts closely monitor the FTSE 100 to understand market trends and make informed investment decisions. The index includes well-known companies from various sectors, such as finance, healthcare, and consumer goods, making it a diverse representation of the UK economy.