A fee (sales charge or load) that investors pay when selling mutual fund shares within a specified number of years, usually five to 10 years. The fee amounts to a percentage of the value of the share being sold. The fee percentage is highest in the first year and decreases yearly until the specified holding period ends, at which time it drops to zero.
Also known as a "contingent deferred sales charge or load."
Source:http://www.investopedia.com/terms/b/back-end-load.asp?partner=TOD9&viewed=1