Psychrometrics is the study of the properties of moist air and the relationships between its temperature, humidity, pressure, and other thermodynamic properties. It involves the use of charts and equations to analyze and predict the behavior of air mixtures, which is crucial in fields like HVAC (heating, ventilation, and air conditioning), meteorology, and environmental engineering. Key concepts include relative humidity, dew point, and enthalpy, which help in understanding how moisture affects comfort and energy efficiency.