Dew Point is the temperature at which the air becomes saturated. Saturation means that the air is holding as much water vapor as possible. As the temperature of the air decreases, the amount of water vapor that it can hold decreases. For example, let's assume that the amount of water vapor in the air remains constant while the temperature decreases. As the air temperature approaches the dew point temperature, the water vapor in the air must condense somewhere.
Under the right conditions, the water vapor will be deposited on the ground as dew. Fog and frost can also be observed when the air temperature and dew point temperature are the same.

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