Once upon a time, there were two types of mutual funds. Load funds were sold through brokers and other middlemen, who charged an up-front commission, usually around 5 percent, which was taken out of the amount invested. No-load funds were sold directly by fund companies to investors, with no commission.

As no-load funds grew, load-fund purveyors began disguising their commissions by creating new share classes with different load and fee structures. Today, load funds might have five or more classes. They all have the same underlying portfolios; the only difference is how and when the investor pays the load.

Today, class A shares typically have a traditional front-end load and the lowest annual expense ratio.

Class B shares typically have no front-end load. Instead, a smaller load is added to the annual expense ratio. B shares also may have a back-end load or "redemption charge" that is levied if the shareholder sells before a certain number of years. Over time, this back end load shrinks and eventually disappears, at which point the shares convert A shares, with the smaller expense ratio.

Class C shares typically have no upfront load. Instead, the load is added to the expense ratio. They may have a small back-end load that disappears in one year. They usually have the highest expense ratio, and never convert to A shares.

Meanwhile, many no-load funds have created share classes that are sold through brokers and other advisers, who are paid a commission. These are often called adviser-class shares.

Both load and no-load companies also have developed special share classes for retirement plans (often called R shares), 529 college savings plans and other types of accounts.

For more, see http://www.nasd.com/InvestorInformation/InvestorAlerts/MutualFunds/UnderstandingMutualFundClasses/index.htm.