The National Association of Securities Dealers' Automated Quotations System is an electronic stock exchange based in New York listing many leading high-tech companies that was formerly owned and operated by the National Association of Securities Dealers (NASD). The exchange's index, the NASDAQ Composite, is a key market benchmark alongside the Dow Jones Industrial Average (DJIA) and the S&P500. In 2007 Nasdaq bought the OMX exchange company which owned and operated exchanges in Stockholm, Helsinki, Copenhagen, Reykjavik and the Baltic states. It bought the Philadelphia Stock Exchange in 2008.
See also: http://www.nasdaq.com/