What is the term for the amount of moisture in the air expressed as a mass per unit volume?

Absolute humidity is the term that refers to the amount of moisture in the air expressed as a mass per unit volume, typically measured in grams of water vapor per cubic meter of air. This measurement gives a direct representation of the moisture content, regardless of temperature or pressure variations.

In contrast, relative humidity expresses how much moisture is in the air as a percentage of the maximum amount the air can hold at a given temperature. Specific humidity measures the ratio of the mass of water vapor to the total mass of the air and water vapor mixture, but it does not represent moisture per unit volume as absolute humidity does. The dew point is the temperature at which air becomes saturated with moisture and forms dew, indicating how much moisture is present, but it does not measure moisture in terms of mass per volume. Thus, absolute humidity is the most precise term for the quantity of moisture in the air in the context provided.