Dry Bulb Temperature: The temperature of the air as measured by a thermometer not affected by moisture or radiation. These values are displayed on the horizontal axis with the ASHRAE psychrometric chart.

Wet Bulb Temperature: Also referred to as the Adiabatic Saturation Temperature. The temperature of air if cooled adiabatically to saturation by evaporation of water. Wet bulb temperature will fall between the dry bulb and dew point temperatures.

Dew Point Temperature: The temperature at which air becomes completely saturated. This is the temperature at which water vapor begins to condense.

Relative Humidity: The percentage of water vapor mass to the water vapor mass at saturation at the same conditions of temperature and pressure.

Frost Point Temperature: Temperature at which frost will appear on exposed surfaces. Frost point temperature is only applicable for psychrometric states where dew point temperature is below freezing. Frost point temperature will be greater than dew point temperature.

Mole Fraction of Dry Air: The ratio of the mass of dry air to the mass of moist air in molar mass units.

Humidity Ratio: Also referred to as the Mixing Ratio. The ratio of the mass of water vapor to the mass of dry air. These values are displayed on the vertical axis with the ASHRAE psychrometric chart.

Grains/Grams of Moisture: The mass of water vapor in a dry air mass sample.

Absolute Humidity: Also referred to as Water Vapor Density. The ratio of the mass of water vapor to the volume of dry air.

Specific Humidity: The ratio of the mass of water vapor to the mass of moist air. Its value will be slightly less than Humidity Ratio.

Degree of Saturation: The ratio of the humidity ratio of air to the humidity ratio of saturated air at the same conditions of temperature and pressure.

Specific Volume: The volume occupied by air per unit mass of dry air. The reciprocal of Specific Volume is Density.

Enthalpy: The total energy content in the air.

Entropy: The energy content in the air that is unavailable for doing useful work.

Cv (Isochoric Specific Heat): The amount of heat required to change air temperature by one degree per unit mass of dry air at constant volume.

Cp (Isobaric Specific Heat): The amount of heat required to change air temperature by one degree per unit mass of dry air at constant pressure.

Velocity of Sound: The speed at which sound travels in the air.