1) Financial market 
Fourth market trading is direct institution-to-institution trading without using the service of broker-dealers. It is impossible to estimate the volume of fourth market activity because trades are not subject to reporting requirements. Studies have suggested that several million shares are traded per day and trading commissions can be avoided. == ...
Refers to the practice of institutional investors trading large blocks of securities directly to avoid brokerage commissions. See: Instinet.
Direct trading in exchange-listed securities between investors without the use of a broker. 
A truncated expression for a P/E ratio that is based on forward (expected) earnings rather than on t
The direct trading of securities between institutional investors without the use of brokers or dealers. 
The market of securities trading without the participation of brokers, thus obviating commission... <a target=_blank href='http://www.finance-glossary.com/terms/fourth-market.htm?id=578&ginPtrCode=00000&PopupMode=false' title='Read full definition of fourth market'>more</a>
The direct trading of large blocks of securities between institutional investors through a computer network. (See INSTINET, third market)