What is the definition of relative humidity?

Relative humidity is defined as the amount of water vapor present in the air compared to the maximum amount of water vapor the air can hold at a given temperature. This concept is critical in meteorology and atmospheric sciences because it helps describe how "humid" or "dry" the air feels to us.

When air is at 100% relative humidity, it means the air is fully saturated with water vapor and cannot hold any more, which can lead to the formation of dew, fog, or clouds. In contrast, at lower percentages, the air can still absorb additional moisture. Understanding this ratio is essential for predicting weather patterns, comfort levels, and various atmospheric phenomena.

The other definitions presented do not capture the interactive nature of the moisture content versus its capacity relative to temperature, which is fundamental to the concept of relative humidity.