A Mass Casualty Incident (often shortened to MCI and sometimes called a Multiple-Casualty Incident or Multiple-Casualty Situation) is any incident in which Emergency Medical Services resources, such as personnel and equipment, are overwhelmed by the number and severity of casualties. Triage is the sorting of patient's treatment based on the severity of their condition. This is an essential part of responding to a Mass Casualty Incident, when limited resources need to be allocated to maximize the number of survivors.