the amount of water vapor in the air, expressed as a percentage of the maximum amount that the air could hold at the given temperature; the ratio of the actual water vapor pressure to the saturation vapor pressure. Abbr.: RH, rh Also called humidity. Cf. absolute humidity, dew point, mixing ratio, specific humidity.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.