Stiffness is an intrinsic physical property quantifying the resistance of a material, system, or biological structure to deformation when an external force or torque is applied. In material science, it is often characterized by the elastic modulus, which relates stress to strain within the elastic limit. Biologically, stiffness describes the structural resilience of connective tissues, such as ligaments and tendons, and is crucial for maintaining proper biomechanical function and joint stability. Variability in stiffness can be assessed through various techniques, including dynamic mechanical analysis, and its measurement is critical in understanding orthopedic health and the potential degradation of load-bearing structures.