When a Stop triggers at your specified price, a Market Order is executed and immediately begins to match the prevailing offers available in the order book, in-line with other orders being executed. During a momentary, rapid price/volume change, such as a fundamental market event causing increased buying/selling at an atypical rate, a large stop order being triggered to perform a market buy/sell, or a large position entering liquidation, the Stop could be triggered and begin executing a Market Order until fulfilled in its entirety.
The nature of a Market Order can increase the risk of the order performing at an average execution price above or below your Stop trigger price. The benefit of a simple Stop is that the order is fulfilled no matter what, including significant trend reversals, but the downside is that price control during a fast moving event can potentially affect the average execution price.
If you would prefer tighter control over your average execution price, consider a Stop-Limit order. This will allow you to set a Stop trigger at a specific price, as with a traditional Stop; however, you also set a LIMIT price at which the order may be executed until. The risk with a Stop-Limit order is that if the market reverses trend significantly and does not recover, your limit may restrict the execution of having the order fulfilled in its entirety.
A Trailing-Stop will trail the market price by your specified “distance” and only trigger the Stop if the distance is reached by market price movement. If this occurs, the Stop is triggered and a Market Order is performed as noted above.