Question

what is reletive motion​

Answer 1

The relative velocity is the velocity of an object or observer B in the rest frame of another object or observer A. Wikipedia

Answer 2

Relative motion is the calculation of the motion of an object with regard to some other moving object. Thus, the motion is not calculated with reference to the earth, but is the velocity of the object in reference to the other moving object as if it were in a static state.