First responder is a term used to describe the first medically-trained responder to arrive on scene of an emergency, accident, natural or human-made disaster, or similar event. Such people may be police or other law enforcement, firefighters, emergency medical services, or lay rescuers. In some countries they may also be people who have had significant first aid training (more than a first aider) who arrive at scenes of emergencies to deal with casualties until more advanced support arrives.