Dissociation constant (Kd) is a type of equilibrium constant that measures the dissociation of a larger object into smaller components. It is the reverse of the association constant, being used to describe the binding affinity between the dissociated components. The inhibitory constant (Ki), on the other hand, is a term used to describe the binding affinity between an inhibitor and its corresponding enzyme, which essentially also represent a dissociation constant. The difference between Kd and Ki is that Kd is a more general, all-encompassing term, whilst Ki is more narrowly used to indicate the dissociation equilibrium constant of the enzyme-inhibitor complex.