Definitions for "DRY AIR"
Air with which no water vapor is mixed. This term is used comparatively, since in nature there is always some water vapor included in air, and such water vapor, being a gas, is dry.
In atmospheric thermodynamics and chemistry, air that contains NO water vapor. Generally, air with low relative humidity.
In physical meteorology this term generally signifies air which is completely dry, i.e. which contains no water vapour.