Climate, decadal averages over one region. Distinguish between relative and absolute humidity. Water vapor can dissolve in air and can be transported around by convection. Moisture can be redistributed over large areas. Water evaporates into air from seas, streams, lakes and soil.
Air can only hold a certain amount of water vapor.
That is it can hold an infinite amount of water. Warm air can hold more water than cold air. Dew and Frost are forms of condensation on solid surfaces by contact. For condensation to occur air has to cool to its dew point. Cold material is more dense.