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 easily. The chart helps engineers and HVAC professionals design systems for heating, ventilation, and air conditioning. By plotting points on the chart, users can determine the state of air and how it changes with different processes, such as cooling or heating. This tool is essential for understanding the relationships between temperature, humidity, and energy, making it invaluable in fields like meteorology and environmental science.