Shear strain is a measure of how much a material deforms when subjected to shear stress. It occurs when forces are applied parallel to a surface, causing layers of the material to slide past one another. This deformation is quantified as the change in angle between two lines originally at right angles, expressed in radians. In engineering and materials science, understanding shear strain is crucial for analyzing the behavior of structures and materials under load. It helps predict how materials will respond to forces, ensuring safety and performance in applications like buildings, bridges, and mechanical components.