Plain English Meaning
When air rises, the pressure on it drops, so it expands. The act of expanding cools it down — even though no heat is being added or taken away.
Full Definition
The decrease in temperature of a parcel of air caused by expansion as it rises into lower-pressure surroundings, with no heat exchanged between the parcel and the air around it.
Context Anchor
Seen in weather and atmospheric stability discussions, especially when explaining rising air, cloud formation, and air moving over terrain.
Derivation
From the Greek 'adiabatos,' meaning 'not to be passed through' — referring to heat not passing in or out. The cooling happens purely from the air expanding, not from heat escaping.
Why Pilots Care
Understanding this helps predict where , , or may form during .