ETF is short for exchange traded fund, which is a type of fund that is traded on public exchanges just like a stock. Compared to a traditional mutual fund, an ETF is priced by the market in real time, and can also be bought and sold instantaneously.
Since ETFs trades more like a stock than a traditional fund, they have also become popular among short-term traders. They can be an ideal way to trade developments in certain industries while avoiding the company-specific risk that comes with trading the stock of a company in that industry. For example, a trader who believes in higher gold prices could trade an ETF of gold mining companies instead of buying the stock of a single gold miner.