condensation nucleus

This term is a specialized technical expression used primarily in meteorology, atmospheric science, and physics. It describes the physical catalyst required for the phase transition of water vapor into liquid droplets, as pure water vapor requires extreme supersaturation to condense on its own.

In a scientific context, the term is used to explain the mechanism of cloud and fog formation. It is distinct from "ice nuclei," which specifically facilitate the formation of ice crystals rather than liquid droplets.