The trading of exchange-listed securities between institutions on a private over-the-counter computer network, rather than over a recognized exchange such as the New York Stock Exchange (NYSE) or Nasdaq. Trades between institutions will often be made in large blocks and without a broker, allowing the institutions to avoid brokerage fees. Taobiz explains Fourth Market For example, when a mutual fund and a pension fund enter into a large block trade with each other, this would generally occur in the fourth market and usually over an electronic communication network. By executing the transaction this way, both parties avoid brokerage and exchange transaction fees. They also avoid the possibility of distorting the market price or the volume traded on an exchange.