A stock index or stock market index is a measurement of a section of the stock market. It is a common tool for investors and financial managers to describe the market and also to compare the returns of specifics investments. It is also one of the most popular types of markets for CFD trading.
A stock index is created from tracking a set of underlying stock prices for that market. For example; the Dow Jones tracks 30 large cap US stocks with each affecting the price of the overall Dow Jones Price.