The frictional force between two moving surfaces which are in contact with each other is called kinetic friction or sliding friction.
Example If a boy apply some pushing force on the box, the box will start sliding on the surface and the friction between the surfaces is called sliding friction.
The force required to keep a body in motion is less than the force required to start the motion, so we can say that sliding friction is less than the static friction.

(i) Explain why the sliding friction is always greater than rolling friction?
(ii) Mention two different examples for sliding friction.