market order :

Used in the context of general equities. Order to buy or sell a stated amount of a security at the most advantageous price obtainable after the order is represented in the trading crowd. You cannot specify special restrictions such as all or none (AON) or good 'til canceled order (GTC) on market orders. See: Limit order.

Market Order :

This is an instruction from a trader to a broker to execute a transaction at the best possible time and for the best available price. A market order does not allow for special requests from the trader such as ‘all or none’.