∙ Relative humidity (RH) indicates the percentage of water vapour present in the air.
∙ It is expressed as a percentage of how much water vapour is present in the air at a particular temperature compared with how much water vapour air actually holds at that temperature.
∙ The maximum amount of water vapour that air can hold increases with the increase in the temperature of the air.
Air at 100% relative humidity holds the maximum amount of water possible at that particular temperature and is said to be saturated.