Definition of Relative Humidity

the ratio of the amount of water in the air at a give temperature to the maximum amount it could hold at that temperature; expressed as a percentage
The content of water vapor in the air, expressed as a percent of the maximum amount of water vapor that the air can hold at the given temperature; also called relative humidity. The capacity of the air to hold moisture increases with temperature, so if the temperature changes without changing the absolute content of the atmospheric moisture, the relative humidity will also change.