An emergency department (ED) is a hospital's 24/7, unscheduled care facility for immediate treatment of serious injuries or sudden illnesses, acting as the healthcare system's safety net for life-threatening conditions, stabilizing patients, and determining next steps like discharge, admission, or transfer. Staffed by specialists in emergency medicine, EDs use triage to prioritize care for all ages, providing rapid diagnosis, stabilization, and critical interventions around the clock.