What refers to the amount of water vapour in the air?

Relative Humidity is the measure of water vapour in air.

It is the ratio of the actual water vapour in air divided by the maximum amount the water the air can hold at the existing temperature and pressure.

It tells how fast or slow the water on the body or in clothes will evaporate or in otherWords is the air dry or humid.

Absolute measure of water vapour in air is called specific humidity.

It can be measured as ratio of mass of water and mass of dry air.