money market fund

Money funds (or money market funds, money market mutual funds) are mutual funds that invest in short-term debt instruments.
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A mutual fund that invests only in short term securities, such as bankers' acceptances, commercial paper, repurchase agreements  and government bills. The net asset value per share is maintained at $1.00. Such funds are not federally insured, although the portfolio may consist of guaranteed securities and/or the fund may have private insurance protection.

A collective investment undertaking that primarily invests in money market instruments and/or other transferable debt instruments with a residual maturity of up to one year, and/or that pursues a rate of return that approaches the interest rates on money market instruments.