Excess humidity built in the form of a thin film of water on a cold surface is called condensation.
You may have noticed this on a humid, hot summer day, when condensation appears on cold glass. If the temperature changes, but no water vapor is added or taken away, the relative humidity will increase as the temperature falls. The relative humidity will continue to rise with falling temperature until the dew point is reached — that is, the temperature at which the relative humidity becomes 100 percent.
Any further decrease in temperature will force some of the vapor to condense as water (when the temperature is above freezing) or as frost (when the temperature is below freezing).
Condensation is the primary reason for window-related call-backs!