Plain English Meaning
An airport that has a control tower with controllers on duty. Pilots have to talk to the tower on the radio and get permission before moving on the runway, taking off, or landing.
Full Definition
An airport with an operating air traffic control (ATC) tower, where pilots must establish two-way radio communication with the tower controller and receive clearances or instructions before taxiing, taking off, or landing within the tower's airspace.
Context Anchor
You will see this term when preparing to taxi, take off, or land at an airport where a control tower is open and directing .