An open-end mutual fund continuously issues and redeems units. If an investor wishes to buy or sell units of an open-end mutual fund, they will do so directly from the fund (as opposed to using a stock exchange). Most mutual funds are open-ended.
Mutual fund that does not have a fixed number of shares outstanding, offers new shares to the public, and buys back outstanding shares at market value.
A fund that sells its shares at net asset value is an open-end fund. It creates shares as investors demand them. Investors buy the shares at their market price. Most mutual funds are open-end funds. Those that aren't are closed-end funds that sell a fixed number of shares to investors.