What does relative humidity represent?

Relative humidity is a measure that expresses the current amount of moisture in the air compared to the maximum amount of moisture that air can hold at a specific temperature. It is calculated as a percentage; thus, when the air is at 100% relative humidity, it is fully saturated with water vapor, meaning it cannot hold any more moisture at that temperature. As temperature increases, the air can hold more moisture, while at lower temperatures, the capacity decreases.

By understanding this concept, it becomes clear why relative humidity is critical in meteorology and weather forecasting, as it directly affects weather patterns, comfort levels, and the likelihood of precipitation. Other choices provide different definitions which don't accurately capture the concept of relative humidity: the total amount of moisture, the specific volume of air, and absolute pressure refer to other measurements related to moisture or atmospheric conditions, but they don't encapsulate the relational aspect of humidity to temperature that relative humidity conveys.