1. people who respond to emergencies or calls for help, especially trained professionals
Usage: often used in the phrase ‘first responders’
2. people who reply or react to something

Examples

• First responders arrived at the accident scene within minutes.
• The firefighters and paramedics are trained responders.
• Emergency responders worked through the night to help victims.
• Police officers are often the first responders to crime scenes.
• Survey responders provided valuable feedback about the new policy.
• Only half of the email responders agreed with the proposal.
• The study included 200 responders from different age groups.