Stop order is opposite to limit order as the order is executed when the market moves to a less favourable position. You can set a specific position when to close your trade because beyond that limit you cannot practically sustain your loss in that trade. This type of stop order is also called Stop loss order, as it restricts your losses.
Sometimes, stop orders are used to open the trade also because from your analysis you predicted that after this less favourable position, the market is going to move to a most favourable position where you can get more profits.
But if Slippage occurs you may lose more. A solution for slippage is guaranteed stops.