Exchange Traded Funds (ETFs) are funds that trade in real-time. ETFs combine some of the advantages of Stocks with those of Open Ended Mutual Funds. ETFs are generally based on indices. Unlike stocks, which cannot be shorted on a 'down-tick', ETFs can be shorted on a down-tick. And unlike Mutual Funds which have no stop and/or limit orders, ETFs can have stop and/or limit orders.