An exchange-traded fund (ETF) is a type of pooled investment security that can be bought and sold much like an individual stock. The main difference between an ETF and a mutual fund is that though a mutual fund is also a pooled investment, it trades only once a day after market close.

An ETF can be structured to track anything from the price of an individual commodity to a large and diverse collection of securities. ETFs can even be designed to track specific investment strategies.