Shear is a difference in speed or direction between neighboring layers of a material. Instead of moving as one solid block, the layers slide past each other, creating stress at the boundary. In fluids and plasmas, shear can trigger waves and instability; in solids, it can deform, crack, or delaminate material when the force is strong enough.
In cyber security, shear matters whenever physical integrity affects trust in a device. Attackers may use mechanical stress to break solder joints, damage sensors, or induce faults in hardware. Defenders account for shear by designing tougher enclosures, using strain relief on cables, adding tamper-evident materials, and testing boards and components under vibration and bending. Even in everyday systems, uncontrolled shear can cause failures that look like random hardware bugs but are actually the result of stress on layered materials.