The ETF (Exchange Traded Fund): The ETF seems like it was created for those active traders that like the way mutual funds perform, but they hated the way they traded.
Liquidity: The ETF is very liquid. It trades like a regular, single stock. Whereas, a mutual fund can only be traded once a day. If you sell a mutual fund, you get the price that it ends in at the end of the day. Active traders that trade on a margin or short sell like the ETF and the way its liquidity.