The definition of a damper in HVAC is a device used to control the flow of air in a heating, ventilation, and air conditioning (HVAC) system. It is usually a metal plate or valve that can be opened or closed to adjust the amount of air that is allowed to pass through the system. Dampers are used to regulate the temperature and humidity in a space, as well as to control the flow of air to specific areas. They are also used to prevent the spread of odors and contaminants throughout the building. Dampers can be manual or motorized, and can be operated remotely or with a switch. They are an important part of any HVAC system, as they help to ensure that the system is operating efficiently and safely.