absolute humidity

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The amount of water vapor present in a unit volume of air, usually expressed in grams per cubic meter.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun meteorology 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. Absolute humidity is usually expressed in grams of water vapor per cubic meter or, in engineering practice, in grains per cubic foot. Because this measure of atmospheric humidity is not conservative with respect to adiabatic expansion or compression, it is not commonly used by meteorologists. (Also called vapor concentration and vapor density). See relative humidity.