Why does an ETF trade all day while a mutual fund only prices once?

An ETF (exchange-traded fund) is bought and sold on a stock exchange like a share of stock, so its price moves continuously throughout the trading day based on supply, demand, and the value of its holdings. You can buy one at 10 a.m. and see a different price at 2 p.m. A traditional mutual fund doesn't trade on an exchange; instead, orders placed during the day all execute at the fund's net asset value (NAV) calculated once after the market closes. That means with a mutual fund you don't know your exact price until end of day. For a long-term index investor the practical difference is small, but ETFs offer intraday flexibility and mutual funds make automatic dollar-based investing simpler.