›a series of numbers published by the Financial Times™ newspaper that shows the changing average value of the share prices of the one hundred British companies on the London Stock Exchange that are being traded the most: the FTSE 100 closed up/downThe FTSE 100 closed 31.6 points down at 2459.3 in today's trading.the FTSE 100 fell/roseThe FTSE 100 fell 5 points to 4,519.5.FTSE 100 shares finished the day flat.