Undrained Shear Strength refers to the maximum shear stress that a saturated soil can withstand without drainage occurring. This property is crucial in geotechnical engineering, especially for cohesive soils like clay, where pore water pressure can significantly affect stability. It is typically measured in terms of cohesion and is essential for assessing the stability of slopes, foundations, and earth structures. In undrained conditions, the soil's effective stress is altered due to changes in pore water pressure, which can lead to failure if the shear strength is exceeded. Engineers often use laboratory tests, such as the unconfined compression test or triaxial test, to determine the undrained shear strength for design and safety evaluations.