What are surface irregularities?

The tiny hills or grooves on the surface of the object are called irregularities of surfaces. The interlocking of irregularities of the two surfaces opposes the motion of one object over the other and gives rise to the force of friction.

 Smooth surfaces have lesser irregularities than Rough ones. The lesser the irregularities, the lesser the tendency to lock. The lesser the tendency to lock with another object, the less is the Frictional force.