The Mohr-Coulomb failure criterion is a fundamental concept in soil and rock mechanics that describes the conditions under which materials fail due to shear stress. It combines the effects of normal stress and shear stress on a material, represented graphically by a failure envelope. This envelope is defined by two key parameters: the cohesion of the material and the internal friction angle. In practical terms, the criterion helps engineers predict when a slope, foundation, or other structures may fail under load. By understanding the relationship between stress and failure, engineers can design safer structures and assess the stability of geological formations.