"... is the quantity of water vapor in the air. Relative humidity is the ration between the actual quantity of watervapor and the amount of watervapor that the air can hold at a given temperature"
EESiFlo North America, Terminology and Glossary: Meteorological Weather Station Terms, Pennsylvania, USA 2002, flowmeterdirectory.com/flowmeter_terminology, (Wthr - Amer) {554}