Plain English Meaning

Altitude is not just one number. There are five different ways pilots talk about how high the aircraft is, and each one means something specific. One tells you what the altimeter reads, one tells you your true height above the sea, one tells you how high you are above the ground right below you, and the last two are used mainly to figure out how the aircraft and engine will perform.

Full Definition

A grouping term for the five distinct ways altitude is measured and referenced in aviation: indicated altitude (read directly from the altimeter when set to the current local pressure), true altitude (actual height above mean sea level), absolute altitude (height above the terrain directly below the aircraft, also called height above ground level or ), (height above the of ), and (pressure altitude for ). Each answers a different question and is used in a different context.