ORDERING - It is a trade instruction given to a broaker who will buy/sell securities for the client/investor. it is a building block of the stock market . it will provide a difference between a profitable trade and a costly trade .
REVOCATION OF TRADE--If an investor wishes to modify the terms of the trade or wishes to cancel his/her existing order and resubmit a fresh order it is mainly a revocation of order
PROBLEMS WITH MODIFICATION-By the time a fresh order is issued market conditions may change adversly. An existing order may get executed before the trader is able to have it cancelled . Correct specification of order is critical moreover speed is the essence of order placement , execution and cancellation