A stop order to sell (or to buy) a security in which subsequent stop orders are placed at progressively higher (or lower) levels as the stock price increases (or decreases). For example, an investor may purchase shares of Union Pacific Corporation at $60 and simultaneously place a stop order to sell the stock if it drops to $58 or below. If the stock rises to $63 without going through the $58 stop price, the investor raises the stop price to $61. Thus, the stop price trails the market price of the stock.