Definition
The temperature to which a sample of air must be cooled, at constant pressure and water vapor content, for it to reach saturation. At the dew point, water vapor in the air begins to condense into visible moisture such as dew, fog, clouds, or frost.
Plain English
The temperature at which the air becomes so cool it can no longer hold all its moisture, and water starts to form on surfaces or in the air.
Context Anchor
Seen in aviation weather, humidity discussions, fog forecasts, and maintenance situations where moisture may collect on aircraft parts.
Derivation
From 'dew,' the moisture that forms on cool surfaces overnight, and 'point,' meaning a specific value on a scale. Together: the exact temperature point at which dew starts forming.
Why Pilots Care
A small temperature-dew point spread signals high humidity and raises the chance of fog, reduced visibility, or icing.
Analogy
Think of a cold drink on a humid day. The glass sweats because the air touching it cools to its dew point, and the moisture in that air condenses on the glass.
Grounding Statement
If the air cools down to its dew point, the extra moisture in that air has to start becoming visible water.
Intuition Check
Dew point is not a time of day or a place where dew forms. It is a temperature.
Example Sentence 1
The METAR showed a temperature of 12°C and a dew point of 11°C, so the pilot expected fog to form shortly after sunset.
Example Sentence 2
With a narrow dew point spread, the pilot checked carburetor heat before descending into humid air.