A dehumidifier is a device that removes excess moisture from the air in a room or home. It works by pulling humid air into the unit through a fan and then passing it over cold coils. As the air cools, water vapor condenses on the coils and is collected in a removable water tank. Dehumidifiers can help reduce humidity levels, which can improve indoor air quality, prevent mold growth, and reduce musty odors. They are particularly useful in damp or humid environments.