The Dow Jones Industrial Average is a stock market index. It is an index that shows how 30 large, publicly owned companies based in the United States have traded during a standard trading session in the stock market.
The S&P 500 is a stock market index which contains the biggest 500 companies in the U.S. This index provides a broad snapshot of the overall U.S. equity market as over 70% of all U.S. equity is tracked by the S&P 500 and it is therefore one of the most important stock indexes of the world.