What is the difference between humidity and relative humidity? Prentice Hall - Science Explorer.

Relative humidity measures water vapor, but it is relative to the temperature of the air. It is a measure of the actual amount of water vapor in the air compared to the total amount of vapor that could exist in the air at that point in time.

Humidity is the measure of water vapor in the air, regardless of the temperature or any other factors. Specific humidity also judges the weight of that water.