An instrument that measures humidity is called a hygrometer. Hygrometers come in various forms, including digital, analog, and even mechanical types. They work by measuring the moisture content in the air, which is essential for applications ranging from meteorology to HVAC systems and agriculture. The most common types include the hair hygrometer, which uses the expansion or contraction of human or animal hair in response to humidity changes, and the electronic hygrometer, which employs sensors for accurate readings. Monitoring humidity levels is vital for comfort, health, and environmental management.