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. There are different types of manometers, including open-tube manometers and differential manometers. Open-tube manometers measure pressure relative to atmospheric pressure, while differential manometers compare the pressure between two points. Manometers are commonly used in various applications, including HVAC systems and laboratory experiments.