Vapor density

From Glossary of Meteorology

vapor density

(Also called absolute humidity.) In a system of moist air, the ratio of the mass of water vapor present to the volume occupied by the mixture; that is, the density of the water vapor component.

Because this measure of atmospheric humidity is not conservative with respect to adiabatic expansion or compression, it is not commonly used by meteorologists.
Compare mixing ratio, specific humidity, relative humidity, dewpoint.