A piezometer is a specialized instrument used in geotechnical and hydrogeological applications to measure the pressure or hydraulic head of groundwater at a specific point in the subsurface. It consists of a sealed pipe or tube inserted vertically into the ground, with an open end submerged in the groundwater. As groundwater levels rise or fall, the pressure within the piezometer changes, and this pressure is measured using a manometer or pressure transducer. Piezometers are essential tools for monitoring groundwater levels, studying subsurface water flow, assessing soil and rock permeability, and ensuring the stability of structures in contact with groundwater, such as dams and retaining walls.