A manometer is a device used to measure the pressure of gases or liquids. It typically consists of a U-shaped tube filled with a liquid, such as mercury or water. When pressure is applied to one side of the tube, the liquid level changes, allowing for the measurement of pressure differences. Manometers can be found in various applications, including HVAC systems, laboratories, and industrial processes. They are essential for ensuring that systems operate within safe pressure limits, helping to prevent equipment failure and maintain efficiency.