As their name indicates, these are funds that invest in the money market (treasury bills, bonds, etc.) in the very short term. Unlike fixed income funds, the investment cannot exceed six months.
Money markets are the markets where cash and assets are traded. Their main objective is to enable both economic agents and investors to preserve part of their wealth in the form of securities that yield an acceptable return and a high degree of liquidity.
Since they invest in highly liquid assets with very low risk, monetary market funds are especially suitable for people who want to carry out very short-term investments as an alternative to deposits.