What is the chief money market in USA known as?

The chief money market in the United States is known as the Federal Funds Market. It is a market where banks lend reserve balances to each other overnight, typically on an unsecured basis. The Federal Funds Market is the primary source of short-term funding for banks and other financial institutions, and it plays an important role in the implementation of monetary policy by the Federal Reserve. The interest rate charged on Federal Funds loans is known as the Federal Funds Rate, which is a key benchmark interest rate in the United States.