The internal friction angle is a measure of the resistance to sliding between particles within a material, particularly in soils and granular materials. It is an important parameter in geotechnical engineering, as it helps determine the stability of slopes, foundations, and earth structures. The angle is typically expressed in degrees and reflects the material's ability to withstand shear stress without failing. This angle is influenced by factors such as particle shape, size, and moisture content. In practice, the internal friction angle is often determined through laboratory tests, such as the direct shear test or triaxial test, which simulate the conditions under which the material will be used.