A number that summarises the price performance of a defined group of securities.
Well-known stock indices include the S&P 500, Dow Jones, Nasdaq-100, Russell 2000, FTSE 100, DAX and MSCI World. Most weight their members by market capitalisation; a few, like the Dow, by share price. Indices serve as benchmarks for funds and as the basis for ETFs.
Price indices measure only price changes; total return indices reinvest dividends.