What is hooke's law? does it apply to elastic materials or to inelastic materials?

When you talk about Hooke's law, it always have to do something with springs. Hooke's Law, from Robert Hooke, saw a relation between the force applied to the spring and the extension of its length. The equation is: F = kx, where k is the spring constant and x is the displacement of the original and stretched lengths. In other words, x is the length of deformation. Hence, the object must be elastic to come up with a displacement or deformation, in the first place. Then, the Hooke's Law is only applicable to elastic materials.