Plain English Meaning

When a pocket of dry air rises, it cools at a steady, predictable rate of about 3 °C for every 1,000 feet it climbs — and warms at the same rate as it sinks. No heat is added or removed; the temperature change comes only from the air expanding or being squeezed.

Full Definition

The fixed rate at which a parcel of unsaturated (dry) air cools as it rises and warms as it descends, due solely to expansion or compression with changing pressure. The accepted value is approximately 3 °C (5.4 °F) per 1,000 feet.

Context Anchor

Seen in weather theory and atmospheric stability discussions, especially when comparing rising air with the air around it.

Derivation

‘Adiabatic’ comes from the Greek adiabatos, meaning ‘not passable’ — referring to heat not passing in or out. ‘Lapse’ means a gradual decrease. So the phrase literally describes how dry air cools off as increases, with no heat exchange involved.