What is the difference between stiffness and modulus in materials testing?

Stiffness refers to a material's resistance to deformation, while modulus measures the material's ability to withstand stress. Stiffness is a property that describes how much a material resists bending or stretching, while modulus quantifies the material's elasticity and stiffness. In materials testing, stiffness is often measured by the material's Young's modulus, which is a specific type of modulus that relates stress to strain.