mutual fund. An investment company registered with the SEC that buys a portfolio of securities selected by a professional investment adviser to meet a specified financial goal (investment objective). Mutual funds can have actively managed portfolios, where a professional investment adviser creates a unique mix of investments to meet a particular investment objective, or passively managed portfolios, in which the adviser seeks to track the performance of a selected benchmark or index. One hallmark of mutual funds is that they issue “redeemable securities,” meaning that the fund stands ready to buy back its shares at their current net asset value (NAV). See also open-end investment company.