All air contains water vapour of varying quantities.
The dew point indicates the amount of moisture in the air. The higher the dew point, the higher the moisture content of the air at a given temperature . Conversely, the dew point of humid air will be higher than the dew point of dry air. A state of saturation exists when the air is holding the maximum amount of water vapour possible at the existing temperature and pressure. Condensation of water vapour begins when the temperature of air is lowered to its dew point and beyond.