Tax money market fund, tax-free money market fund. Tax money market fund: it mainly invests in short-term and high-grade money market securities with a maturity of less than 90 days. Divided into: government tax money market funds, mainly investing in US Treasury bonds and other financial products guaranteed by the government; Non-government tax money market funds mainly invest in non-government money market instruments such as commercial bills and large negotiable certificates of deposit; Tax-free money market funds mainly invest in government securities with an average maturity of 90 days, which can be exempted from federal taxes and sometimes state and local taxes; And national tax-free money market funds invested in all parts of the United States.