Shear stress is a measure of how much force is applied parallel to a surface area. It occurs when layers of material slide past each other, which can happen in solids, liquids, and gases. The formula for shear stress is the force divided by the area over which it acts, typically expressed in units like pascals (Pa). In engineering and physics, understanding shear stress is crucial for designing structures and materials. For example, when a beam supports a load, shear stress helps determine if it can withstand the forces without failing. Proper analysis ensures safety and functionality in various applications.