Shear force is a type of internal force that acts parallel to the surface of a material. It occurs when two opposing forces are applied in a way that causes one part of an object to slide over another. This force is crucial in understanding how structures like beams and bridges respond to loads. In engineering, shear force is important for ensuring the safety and stability of structures. Engineers calculate shear forces to determine whether materials can withstand applied loads without failing. Understanding shear force helps in designing safe buildings and other constructions, preventing potential structural failures.