Definition
The vertical distance of an aircraft or object above a specified reference, such as mean sea level (MSL), the ground (AGL), or a pressure datum. In aviation, altitude is normally expressed in feet and is one of the primary parameters pilots monitor and report.
Plain English
How high the aircraft is, measured from a chosen starting point — usually sea level or the ground below.
Context Anchor
Seen on flight plans, cockpit displays, clearances, charts, weather reports, and performance discussions.
Derivation
From the Latin altus, meaning 'high.' The same root gives us 'altitude' and 'altimeter.' Knowing the root reinforces that the word is purely about height — not speed, not position, just how high something is.
Why Pilots Care
Accurate altitude keeps the aircraft clear of terrain, maintains required separation from other traffic, and satisfies airspace and regulatory requirements.
Intuition Check
Do not assume altitude always means height above the ground. In aviation, altitude usually depends on the reference level being used, often sea level unless another reference is stated.
Example Sentence 1
ATC instructed the pilot to maintain an altitude of 6,500 feet until reaching the next waypoint.
Example Sentence 2
ATC instructed the aircraft to climb and maintain an altitude of 8,000 feet.