In general, hysteresis describes the behavior of a system in which an output variable is dependent on an input variable and also on the previous state of the output variable. In such a system, the output variable assumes different values when the input variable increases from when it decreases.
Hysteresis occurs with the dynamic contact angle, as the contact angle usually assumes different values in the course of wetting (advancing angle) from de-wetting (receding angle). The degree of hysteresis is a measure of the roughness of the surface.

Measurement of advancing angle and receding angle