Definition
The vertical distance of a level, point, or object considered as a point, measured from mean sea level (MSL). This is the ICAO standard definition of altitude, which fixes the reference as MSL unless otherwise stated.
Plain English
How high something is, measured straight up from average sea level. When ICAO says 'altitude,' that's the reference point being used.
Context Anchor
Seen in altimeter readings, charts, flight plans, and air traffic control altitude assignments.
Derivation
From Latin 'altitudo,' meaning height or depth, from 'altus' (high). 'ICAO' marks this as the International Civil Aviation Organization's standardized definition, used so that pilots and controllers worldwide share one common meaning.
Why Pilots Care
Provides the consistent vertical reference needed for safe separation from terrain and other traffic when flying under ICAO rules.
Grounding Statement
If an aircraft is at 5,000 feet altitude, it is 5,000 feet above the sea-level reference, even if the ground below is much closer or much farther away.
Intuition Check
Do not assume altitude means height above the ground. In this ICAO meaning, altitude is measured from mean sea level.
Example Sentence 1
Per ICAO, the aircraft's altitude is reported as 8,500 feet, meaning 8,500 feet above mean sea level.
Example Sentence 2
ICAO defines altitude as measured from mean sea level to ensure uniform vertical separation worldwide.