Market Not Held is a type of order that gives the floor broker discretion over the time and price of execution.
Applying "Market Not Held" to Securities Exams:
A large firm or investor may give a floor broker time and price discretion over an order by designating the order market not held. A floor broker will often have better visibility as to the market conditions in a security and may be able to execute the order at more favorable prices. If a better price is available in the market place after the order is executed the floor broker can not "be held" responsible for the fact that a better price was available later.