1) It triggers some stock orders 
A stop price is the price in stop order that triggers creation of market order. In the case of a Sell on Stop order, when the market reaches or falls below the Stop Price a market sell order will be triggered. For Buy on Stop orders, the stop price triggers the creation of a market buy order when the market price of the stock rises to or above the...
The price at which a Stop order is triggered. For purchases the stop price acts as a minimum price you will pay if an investment is made and for sales the stop price acts as the maximum price you will receive if a holding is sold.
the price at which a stop order is activated.