Psychrometry deals with the thermodynamic properties of gas-vapor mixtures. Air-water vapor mixtures are the most common systems studied because of their importance in heating, ventilating, air conditioning, and weather reporting.
Students of engineering are introduced to the subtleties of psychrometry in their thermodynamics courses. But we are all exposed to psychrometry any time we watch weather reports on television. Your favorite meteorologist probably speaks about the relative humidity, dry bulb temperature, and dew point temperature.