A stop order is an order to buy or sell once a pre-defined price is reached. When the price is reached, the stop order becomes a market order and is executed at the best available price. It is important to remember that stop orders can be affected by market gaps and slippage, and will not necessarily be executed at the stop level if the market does not trade at this price. A stop order will be filled at the next available price once the stop level has been reached. Placing contingent orders may not necessarily limit your losses.