Amount of water vapor in the air
Humidity means water vapor in the air, but not to liquid droplets in fog, clouds, or rain. Deserts usually have low humidity, and tropical regions have high humidity. The word "humid" often means that the humidity is high, which gives the feeling of being very damp (wet air), stuffy, or even sweltering when the temperature is also high. When the humidity is low, the air can be said to be "not humid" or "dry."
Higher humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin.
Humidity affects the rate of evaporation. With a higher humidity, the rate of evaporation is less.