A market of large borrowers and lenders

The money market of the United States is dominated by a relatively small number of large financial institutions. No more than a hundred commercial banks in New York, Chicago, San Francisco, Dallas, and a handful of other money centers are at the heart of the market. These large banks account for the bulk of federal funds trading through which money market transactions are carried out. In addition, securities move readily from sellers to buyers through the market-making activities of about three dozen major government security dealers and a handful of dealers and brokers in commercial paper, bankers‘acceptances, certificates of deposit, and federal funds. And, of course, the U.S. government plays a major role in this market as the largest borrower and as regulator, setting the " rules of the game." the federal reserve system, operating principally through the trading disk at the federal reserve bank of new York, is in the market nearly every day, either supplying funds to banks and securities dealers through purchases of securities or absorbing funds through security sales.
Individual transactions in the money market involve huge amounts of funds. Most trading occurs in multiples of a million dollars. For this reason the money market is often referred to as a "wholesales" market for funds, as opposed to the "retail" market where consumers and small businesses borrow.