Has the meaning given in Rule 8.4.1 of The Capacity Market Rules 2014. A Settlement Period in which a System Operator Instigated Demand Control Event occurs where such event lasts at least 15 continuous minutes (whether the event falls within one Settlement Period or across more than one consecutive Settlement Periods, and where the event falls across multiple consecutive Settlement Periods, each of those Settlement Periods will be a “System Stress Event”).