Stability is the property of the atmosphere that describes the ability for air to resist vertical motion. A stable atmosphere makes vertical movement difficult, while an unstable atmosphere encourages vertical movement. An unstable atmosphere often leads to significant turbulence, vertical clouds, and severe weather.
Stability is directly determined by lapse rate. Warm, humid conditions at the surface with cold, dry air aloft are key factors of an unstable atmosphere. A temperature inversion is a mark of a very stable atmosphere.