an index based on the market price of about 840 companies listed on the London Stock Exchange (it includes the companies on the FTSE 100 Index, the 250 Index, plus companies in other indices) nounan index based on the market price of about 840 companies listed on the London Stock Exchange (it includes the companies on the FTSE 100 Index, the 250 Index, plus companies in other indices)(NoteAlso simply called the All-Share Index.)