An order placed with a broker to sell a security when it reaches a certain price. A stop-loss order is designed to limit an investor’s loss on a position in a security. Although most investors associate a stop-loss order only with a long position, it can also be used for a short position, in which case the security would be bought if it trades above a defined price. A stop-loss order takes the emotion out of trading decisions and can be especially handy when one is on vacation or cannot watch his/her position. However, execution is not guaranteed, particularly in situations where trading in the stock is halted or gaps down (or up) in price. Also known as a “stop order” or “stop-market order.”