Wiktionary
n. (context finance English) A mutual fund (qualifier: US) that invests almost exclusively in short-term money market instruments whose value is deemed unlikely to fluctuate.
Wikipedia
A money market fund (also called a money market mutual fund) is an open-ended mutual fund that invests in short-term debt securities such as US Treasury bills and commercial paper. Money market funds are widely (though not necessarily accurately) regarded as being as safe as bank deposits yet providing a higher yield. Regulated in the United States under the Investment Company Act of 1940, money market funds are important providers of liquidity to financial intermediaries.
Usage examples of "money market fund".
But the bank would credit the money to its overnight money market fund and earn approximately five and one half percent or seven thousand and, um, eighty-two dollars.