A legal, but frowned-upon practice, whereby traders attempt to gain short-term profits from buying and selling mutual funds to benefit from the differences between the daily closing prices.

Don't confuse market timing with mutual fund timing. Market timing is a very acceptable practice of trying to predict the best time to buy and sell stocks.

Watch: Mutual Funds

Mutual fund timing has a negative effect on a fund's long-term investors, as they will be subjected to higher fees due to the transaction costs of the short-term trading. In order to prevent this practice, most mutual funds impose a stiff short-term trading penalty, known as a redemption fee, upon the sale of funds that are not held for a minimum period of time, which generally ranges from 90 days to one year.

In September of 2003, some mutual fund companies were investigated for permitting hedge funds to "time" mutual funds purchases. These hedge funds paid the mutual fund companies money for the right to buy and sell funds on a short-term basis without any short-term penalties.