Definition
An airspace of defined dimensions within which air traffic control service is provided to IFR flights and to VFR flights in accordance with the airspace classification. The ICAO definition applies to airspace Classes A, B, C, D, and E.
Plain English
A specific block of sky where ATC actively provides separation and traffic services to aircraft. The level of service depends on which class of airspace it is.
Context Anchor
Seen in airspace classification, chart use, flight planning, and international aviation references.
Derivation
ICAO stands for the International Civil Aviation Organization, the United Nations body that sets global aviation standards. The [ICAO] tag means this is the international definition, which may differ slightly from the FAA domestic definition of the same term.
Why Pilots Care
Entry normally requires radio contact and may require an ATC clearance, directly affecting route choice and workload.
Intuition Check
Do not assume controlled airspace means every aircraft is being personally directed every second. It means air traffic control service is available and applied according to that airspace class.
Example Sentence 1
Once they climbed above 18,000 feet they were in Class A controlled airspace and required a clearance to operate there.
Example Sentence 2
VFR traffic in controlled airspace must maintain two-way radio contact with ATC when operating in Class C or D.