thermocline

An intermediate layer of oceanic water in which temperature decreases more rapidly with depth than in the layers above and below it.

A layer in a large body of water, such as a lake, that sharply separates regions differing in temperature, so that the temperature gradient across the layer is abrupt.

A layer within a large body of water sharply separating portions of it which differ in temperature, so that the temperature-gradient through the layer is very abrupt.

A layer within a body of water or air where the temperature changes rapidly with depth.