Plain English Meaning
The help and instructions pilots get from controllers on the ground who watch over aircraft, keep them apart, and guide them safely from takeoff to landing.
Full Definition
The services provided by the Federal Aviation Administration's network of controllers and facilities to promote the safe, orderly, and expeditious flow of air traffic. ATC services include separating aircraft, issuing clearances and instructions, providing traffic advisories, sequencing arrivals and departures, and assisting pilots during emergencies. These services are delivered through control towers, terminal radar approach control facilities (TRACONs), air route (), and , each handling a or .