Investopedia explains Money Market

The money market is used by a wide array of participants, from a company raising money by selling commercial paper into the market to an investor purchasing CDs as a safe place to park money in the short term. The money market is typically seen as a safe place to put money due the highly liquid nature of the securities and short maturities, but there are risks in the market that any investor needs to be aware of including the risk of default on securities such as commercial paper