What does relative humidity measure?

Relative humidity is a measure of how much water vapor is present in the air compared to the maximum amount of water vapor that the air can hold at a given temperature, which is referred to as the saturated vapor density. This ratio is expressed as a percentage. When relative humidity is high, it means that the air is close to being saturated with moisture, which can affect weather conditions and comfort levels. Understanding relative humidity is essential in many fields, including meteorology, as it impacts precipitation, cloud formation, and overall climate conditions.

The other options address related concepts but do not define relative humidity accurately. Measuring the total amount of moisture in the air pertains more to absolute humidity, while the amount of evaporation pertains to dynamics of moisture changes rather than a direct comparison of vapor densities. The temperature at which moisture condenses is known as the dew point, which is a different aspect of atmospheric moisture.