relative humidity

This term is a technical measurement used primarily in meteorology, HVAC engineering, and environmental science. It describes the saturation level of the air rather than the absolute mass of water vapor, meaning the value changes if the temperature changes, even if the moisture content remains constant.

Because it is a specific scientific measurement, it is treated as an uncountable noun. It is almost always paired with verbs like "increase," "decrease," "reach," or "maintain," and is expressed as a percentage.