Stock Market
S&P 500 is an index that is owned and operated by a division of McGraw-Hill known as Standard & Poor's. S&P 500 is a free-float capitalization-weighted index. This is published since 1957 and consists of 500 large-cap common stocks actively traded in the United States. These stocks are only those which are largely held by public and which trade on either NASDAQ OMX or NYSE Euronext. S&P 500 is a part of S&P 1200 and S&P Global 1500 which are two larger indices.
The rules for selection for listing at S&P 500 are very similar to Dow 30. There are just 5 non-US companies included in the index. The companies which do not have enough liquidity or which are not publicly held are excluded or left out of the index. The index also leaves out the companies with extremely high stock price as they are difficult to trade. S&P 500, during trading sessions is updated every 15 seconds.
NASDAQ is the NASDAQ stock market, an American stock exchange. Earlier it was known as National Association of Securities Dealers Automated Quotations, but now it is no longer used. It is an equity securities trading market with an electronic screen based phenomenon and is the largest such electronic equity securities trading market in the US.
The Dow Jones Industrial Average is also known as Dow 30 or Dow Jones or simply Dow. This is one of the major stock market indices and was created by Wall Street Journal editor and one of the co-founders of Dow Jones & Company, Charles Dow along with Edward Davis and Charles Milford Bergstresser on May 26, 1896.