The idea behind a mutual fund is simple: Many people pool their money in a fund, which invests in various securities. Each investor shares proportionately in the fund's investment returns -- the income (dividends or interest) paid on the securities and any capital gains or losses caused by sales of securities the fund holds.

Every mutual fund has a manager, also called an investment adviser, who directs the fund's investments according to the fund's objective, such as long-term growth, high current income, or stability of principal. Depending on its objective, a fund may invest in stocks, bonds, cash investments, or a combination of these financial assets.