An exchange traded fund is an investment vehicle or security that behaves like a stock in that it can be regularly traded on any number of exchanges, but specifically tracks an index or indexes, commodities, bonds, or other assets. Its daily price may change during the trading day, as its shares are constantly being bought and sold by investors, so its net asset value is not calculated on a daily basis, as occurs with a mutual fund that determines its net asset value at the close of the market each day. ETFs tend to trade near their current net asset value during the course of a trading day.