The atmospheric air around us, due to the continuous evaporation of water from the surface of the oceans, seas, reservoirs, moist soil and plants, always contains water vapor. The more water vapor is present in a certain volume of air, the closer the vapor is to the saturation state. On the other hand, the higher the temperature of the air, the more water vapor is required to saturate it.
Depending on the amount of water vapor at a given temperature in the atmosphere, the air is of different degrees of humidity.