A psychrometer is a device used to measure the humidity in the air. It consists of two thermometers: a dry bulb thermometer that measures the air temperature and a wet bulb thermometer that has a moistened wick. By comparing the temperatures from both thermometers, one can determine the relative humidity of the air. Psychrometers are commonly used in meteorology, HVAC systems, and various industrial applications. They help in understanding moisture levels, which is crucial for weather forecasting, climate control, and ensuring optimal conditions for processes like drying and storage of materials.