What Is ICAO? Definition & Meaning in Aviation
ICAO (the International Civil Aviation Organization) is the United Nations agency that sets international standards for civil aviation safety, air navigation and airport operations.
In plain language
It was created by the 1944 Chicago Convention and assigns the four-letter airport codes and three-letter airline codes used by pilots and air traffic control.
Example
Pakistan is a member state; the standards it follows for air navigation come from ICAO.
Why it matters
ICAO’s standards are what allow aircraft from any country to fly into any other. The codes it issues are what you see on weather reports and trackers.