Dow Jones, FTSE 100 - What is an index? - MoneyWeek Investment TutorialsThis story was updated at 4:55 p.m. EDT.U.S. stocks closed Friday with huge losses in the wake ofBritains vote to quit the European Union,the biggest shock to the global financial system since the 2008 financial crisis.The Dow Jones Industrial Average finished the day with a loss of610 points, or 3 percent, having fallen as much as 655 points in the...