relative humidity

relation between the amount of vapor in a unit of air and the maximum amount the air can absorb

Relative humidity is a term used to describe the amount of water vapor that exists in a gaseous mixture of air and water.
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Relative humidity n. The ratio of the amount of water vapor in the air at a specific temperature to the maximum amount that the air could hold at [more]Relative humidity - Community and Resources

Noun
1. 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
(hypernym) ratio

A dimensionless ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Since the latter amount is dependent on temperature, relative humidity is a function of both moisture content and temperature. As such, relative humidity by itself does not directly indicate the actual amount of atmospheric moisture present. See dew point .