S&P 500

A market-capitalization-weighted index of 500 leading U.S. public companies, maintained by S&P Dow Jones Indices. Widely regarded as the single best gauge of American large-cap equity performance, the S&P 500 is the benchmark against which most fund managers are measured. The index was created in 1957, though S&P had been tracking smaller baskets of stocks since 1923. More money is indexed to the S&P 500 than any other equity index in the world.