A mutual fund that invests in assets that are easily converted into cash and which have a low risk of price fluctuation. This may include money market holdings, Treasury bills, and commercial paper. Money held in money market funds is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency. Money market funds seek to preserve the value of your investment at $1.00 a share. However, it is possible to lose money by investing in a money market fund.