Plain English Meaning
AMTs are the qualified people who look after aircraft on the ground — checking them, fixing problems, and signing off that they are safe to fly again.
Full Definition
Aviation maintenance technicians are FAA-certificated personnel trained and authorized to inspect, service, repair, and approve aircraft and aircraft components for return to service. Their work is governed by FAA regulations and aircraft manufacturer data, and their certification typically covers airframe, powerplant, or both (commonly called A&P).