What Is the Difference Between Dew and Frost?
Dew and frost are actually the same phenomenon, except that dew occurs when the air temperature is above freezing while frost occurs when it is below. Both are condensation that occurs when moisture held in the air is cooled to a point that the air can no longer support it.
True frost occurs when the temperature is low enough for the water vapor in the air to sublimate, or go from a gaseous state to a solid without first becoming a liquid, directly onto objects in the environment. Liquid accumulation that later freezes is not frost, but frozen rain or dew.