The statement that motion is relative is an important concept in physics. The meaning behind this statement is that the motion of an object is relative to either the frame of reference of the observer, or to another distinct frame of reference. This is important because the observed motion may appear different depending on which frame of reference it is being observed from. Because of this, relative velocity must be used to explain movement within a certain frame of reference. An example of this would be a person riding on a bus who we will call Bob. People on the bus observing Bob sitting in his seat, would observe that Bob is not be moving relative to the movement of the bus. However, these same people can observe that Bob is moving relative to an object located outside the bus. Hope this helps!