A psychrometric chart is a graphical representation of the physical and thermal properties of moist air. It displays various parameters such as temperature, humidity, and enthalpy, allowing users to analyze air conditions and processes. The chart helps engineers and HVAC professionals design systems for heating, ventilation, and air conditioning by visualizing how air properties change with different conditions. The chart consists of curved lines representing relative humidity, dry bulb temperature, and wet bulb temperature. By plotting points on the chart, users can determine the state of air and make informed decisions about energy efficiency and comfort in indoor environments.