What term describes the actual amount of water vapor in a mixture of air and water?

The term that accurately describes the actual amount of water vapor in a mixture of air and water is absolute humidity. This measurement is expressed as the mass of water vapor present in a given volume of air, typically in grams per cubic meter. It provides a direct indication of the water vapor content in the air, regardless of the air's temperature.

Relative humidity measures the current amount of water vapor in the air compared to the maximum amount the air can hold at a given temperature, but does not provide a specific mass. Specific humidity is the ratio of the mass of water vapor to the total mass of the air-water mixture, also expressed in grams of water vapor per kilogram of total air. Vapor pressure refers to the pressure exerted by the water vapor in the air, not its actual amount. Thus, absolute humidity is the most direct measure of the water vapor present.