Dew point temperature is the temperature when the water vapour present in air begins to condense.

The dew point can also be defined as the temperature at which the outside air becomes completely saturated with moisture.

  • If the dew-point temperature is close to the dry bulb temperature –  the relative humidity is high
  • If the dew point is well below the dry bulb temperature – the relative humidity is low

If the relative humidity is 100% then the dew point temperature will be the same as the dry bulb temperature.

Also see the answer to the question: What is the difference between wet-bulb and dry-bulb temperature?