The percentage of water vapor in the air compared to the maximum amount of water vapor that air can contain at a particular temperature.

Relative humidity %

Explanation:

The relative humidity is the percentage of the water vapor content at a particular temperature and pressure to the maximum amount of water vapor content the air can hold at those conditions. When the relative humidity of the air becomes 100% then there occurs precipitation on the earth from the atmosphere (specifically troposphere, which accounts for the weather changes). We might have experienced excessive sweating even on a relatively less hotter day of a summer which is on account of increased relative humidity.