A closed-end fund (CEF) is a fund that doesn't redeem and sell new shares continuously, as open-end funds do. It is traded at a stock exchange, as if it was ordinary stock, and usually sells at a premium or discount with respect to the value of its underlying assets (i.e. net-asset value o NAV). An exchange-traded fund (ETF) also trades in a stock exchange, like a CEF. But it is open-end, like a mutual fund, so it doesn't suffer price variations with respect to its NAV. ETFs and CEFs are the vehicles of choice for fund investors who operate through a stock broker.
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