Source : Webster's Revised Unabridged Dictionary (1913)

Stop order \Stop order\ (Finance)
   An order that aims to limit losses by fixing a figure at
   which purchases shall be sold or sales bought in, as where
   stock is bought at 100 and the broker is directed to sell if
   the market price drops to 98.

Source : WordNet®

stop order
     n : an order to a broker to sell (buy) when the price of a
         security falls (rises) to a designated level [syn: {stop-loss
         order}]