The temperature of the air when it is cooled to saturation. (When saturation is reached, the air cannot hold any additional moisture, and any excess moisture condenses as dew on surface features such as grass or plants).
The temperature at which moist air becomes saturated (100% relative humidity) with water vapor when cooled at constant pressure.
The temperature to which air must be cooled for condensation to begin, assuming there is no air pressure or moisture content change. At that temperature dew begins to form, and water vapor condenses into liquid. Dew point temperature is a measure of the amount of water vapor in air.