Vapor
Vapor (US English) or vapour (British English) is the gaseous state of matter.
Although vapor and gas are frequently used interchangeably, vapor often carries the connotation of gaseous matter in a state of equilibrium with identical matter in a liquid or solid state. See the entry on vapor pressure for more information on this topic.
The constituent atoms or molecules of a vapor possess vibrational, rotational, and translational motion. More information can be found under the entry of the Kinetic theory of gases.