what's the difference between humidity and relative humidity?

Answer 1

Humidity can be thought of as an absolute number, independent of actual temperature.

On a very cold day, for instance, the humidity outside would be much larger than the humidity from the same air mass inside at room temperature.

Depending on the outside temperature the humidity may be say, 50%. The same are mass inside, warmed to room temperature may be in the single digits.

Answer 2

There is absolute humidity and relative humidity.Absolute humidity is the measure of water vapor in the air. Relative humidity is the measure of humidity compared to how high the humidity can possibly be in the area.

Answer 3

As difined by the National Weather Service
http://www.srh.noaa.gov/srh/jetstream/append/glossary_a.htm

Humidity
Generally, a measure of the water vapor content of the air. Popularly, it is used synonymously with relative humidity.

Relative Humidity
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.

Answer 4

By humidity we always mean the Relative Humidity only.But, actually there is a difference in what they refer to.
The presence of water vapour(moisture) in the atmosphere attributes to it a property known as humidity.Therefore if water vapour is present,the air is said to be humid,- otherwise the air is dry.So humidity is a property of the atmosphere which indicates simply the presence of moisture.
Relative Humidity is the ratio of the amount of water vapour present in the air to the amount of water vapour required to saturate the air at that temperature.This is expressed as a percentage.In short Relative Humidity is known as the degree of saturation.
In other words,Humidity indicates the presence of water vapour in atmosphere whereas Relative Humidity gives the percentage of water vapour in the atmosphere for a particular temperature.