The FT Index, also known as the FTSE (Financial Times Stock Exchange) index, is a stock market index that measures the performance of the top 100 companies listed on the London Stock Exchange. The index is commonly referred to as the UK 100 or the Footsie. The term "Footsie" is a blend of the words "FT" and "indices." Other synonyms for the FT Index include the FTSE 100, the FTSE All-Share Index, and the FTSE World Index. The FT Index is considered a leading indicator of the UK economy's health and is closely monitored by investors, analysts, and business leaders.