Money Market Fund

A money market fund is a mutual fund holding very short-term, high-quality debt, designed to keep a stable value while paying prevailing short-term rates. It is an investment, not a deposit: there's no government insurance, and 'breaking the buck' — falling below a $1 NAV — has happened, triggering a run in 2008. Government-only funds are the most conservative version, and yields track policy rates far faster than bank savings rates do.