The following is a 3rd party contribution
Index trading online enables traders to invest in major national indices such as the French CAC40, the German DAX30, and the British FTSE 100. The 3 major Wall Street stock indices are the DJIA (Dow Jones Industrial Average), the S&P 500 (Standard & Poor’s 500) and the Nasdaq.
The Dow usually gets most of the attention, but the S&P 500 is more important to traders and is generally considered the most representative of the U.S. economy, as it is made up of 500 leading companies.
Founded on March 4th, 1957, the S&P 500 represents about 80% of U.S. market capitalisation. It is the most accurate tool for investors to monitor the overall health of the U.S. economy and is widely accepted as the best gauge of large cap equities. Worldwide indices are highly correlated and U.S. markets are usually the leading indicators of global economic forces, with European and Asian markets often following their performance.