What is friction? What is impending motion?

(N/A) Friction is a contact force that opposes the relative motion or the tendency of relative motion between two surfaces in contact. It acts parallel to the surfaces and is caused by the microscopic irregularities and intermolecular forces between the surfaces.
Impending motion refers to the state where an external force is applied to an object,but it has not yet started to move. The object is on the verge of sliding,and the static friction acting on it has reached its maximum value,known as limiting friction.