What is meant by rolling friction ?

Explanation

When a wheel rolls on a surface the point of contact with surface is always at rest Since the point of contact is at rest there is no relative motion between the wheel and surface . Hence the frictional force is very less . At the same time if an object moves without a wheel there is a relative motion between the object and the surface. Due to teh elastic nature of the surface at the point of contact there will be some deformation on the object at this point on the wheel . Due to this deformation there will be minimal fricition between wheel and surface . In fact rolling friction is much smaller than kinetic friction.