<human>:  What is the definition of a mutual fund?
<bot>: A mutual fund is a professionally managed investment fund that pools money from many investors to purchase securities. These securities may include stocks, bonds, money market instruments, and other types of investments. The fund's portfolio is structured and maintained to match the investment objectives stated in the fund's prospectus. Mutual funds give small investors access to diversified, professionally managed portfolios at a relatively low cost.