Condensation

From GAWDAwiki

Condensation is the process of forming a liquid from its vapor under a change in temperature or pressure.^[1]

Condensation usually occurs when a parcel of rising air expands and cools. If it cools enough, some of the gaseous vapor molecules clump together faster than they are torn apart from their thermal energy. A very important part of this process is the release of the latent heat of condensation. This is the heat that was absorbed when the liquid originally evaporated.^[2]

References

1. http://www.bocindustrial.co.uk/bocindustrial/technical/glossary/a.asp
2. http://www.weatherquestions.com/What_is_condensation.htm