An exchange-traded fund (ETF), also known as an exchange-traded product (ETP), is an investment fund traded on stock exchanges, much like stocks. An ETF holds assets such as stocks, commodities, or bonds and trades at approximately the same price as the net asset value of its underlying assets over the course of the trading day. Most ETFs track an index, such as the S&P 500 or MSCI EAFE. ETFs may be attractive as investments because of their low costs, tax efficiency, and stock-like features.

以沪深300为例，就是基金一个份额里含有沪深300的各个股票按各自权重，所以你买一股基金就相当于买了微缩过的300个股票。好处就是方便，自己不用去整300个股票，然后按比例买。

谢谢各位热心人！
欢迎更多补充

我的理解  就是  一种 股票型 开放式基金。。。   它和 开放式的区别在于  可以进行 买卖， 并且市价 对 净值偏离，和 封闭式的区别 在于 他本质还是开放式  可以自由购买 赎回。。。