When an external force is applied, the body gets distorted from it's original shape. The body takes some time to regain into it's original shape. Therefore, the delay or the time that is taken for the body to acquire it's original shape after the deforming force is removed is called 'elastic after effect'.
What is the nature of inter-atomic or inter-molecular forces?
Inter-atomic or inter-molecular forces are electrostatic in nature.
Adhesive force is the attractive force between two unlike molecules. They are caused by forces acting between two substances like electrostatic force (attraction due to opposing charges), mechanical force etc.