The Nasdaq Composite is a stock market index that includes almost all stocks listed on the Nasdaq stock exchange. Along with the Dow Jones Industrial Average and S&P 500, it is one of the three most-followed stock market indices in the United States. The composition of the NASDAQ Composite is heavily weighted towards companies in the information technology sector. The Nasdaq-100, which includes 100 of the largest non-financial companies in the Nasdaq Composite, accounts for about 80% of the index weighting of the Nasdaq Composite. The Nasdaq Composite is a capitalization-weighted index; its price is calculated by taking the sum of the products of closing price and index share of all of the securities in the index. The sum is then divided by a divisor which reduces the order of magnitude of the result. Wikipedia