An exchange-traded fund (ETF) is a set of securities that are traded on an exchange in the same way as stocks.
ETF share prices fluctuate throughout the day as ETFs are bought and sold; this is different from mutual funds, which only trade once a day after the market closes.
ETFs can contain all types of investments, including stocks, commodities or bonds; some offer US-only assets, while others offer international assets.
ETFs offer low expense ratios and lower brokerage fees than buying shares individually.