Question

What is meant by combination of motion

Answer 1

Many times we will know the velocity of an object, or its angular velocity, but not both. ... Rolling without slipping is defined as the special case of combined rotational and translational motion in which there is no relative motion between the object and the surface with which it is in contact.

Answer 2

It means
Rolling without slipping is defined as the special case of combined rotational and translational motion in which there is no relative motion between the object and the surface with which it is in contact