Definition
Authorization issued by an air traffic control unit for an aircraft to proceed under conditions specified by that unit. Under ICAO usage, the term is commonly abbreviated to 'clearance' when used in the appropriate context, and the type of clearance is normally identified by a prefix such as taxi clearance, takeoff clearance, departure clearance, en route clearance, approach clearance, or landing clearance.
Plain English
Permission from air traffic control for an aircraft to do something specific, such as taxi, take off, fly a route, approach, or land, under the conditions ATC sets. The ICAO version is the international standard wording used outside the United States.
Context Anchor
Pilots encounter air traffic control clearances on the radio before taxi, takeoff, route changes, altitude changes, approaches, and landings.
Derivation
Clearance' comes from 'clear,' meaning free of obstruction. A clearance from ATC means the airspace or surface ahead has been arranged so the aircraft is free to proceed under the stated conditions. The '[ICAO]' tag marks this as the International Civil Aviation Organization's standard wording, used worldwide.
Why Pilots Care
A pilot must have and follow this authorization to legally enter controlled airspace or fly under IFR; operating without it risks loss of separation.
Intuition Check
A clearance is not a blanket statement that everything ahead is safe. It is permission to proceed under specific conditions, while the pilot still remains responsible for the aircraft.
Example Sentence 1
The crew received their en route clearance from the tower before pushing back from the gate.
Example Sentence 2
Before entering the busy terminal area, the crew requested and received an air traffic control clearance for the arrival route.