Rest & Motion Relative terms?

 Frame of Reference - A frame of reference is another object or scene with respect to which we compare an object's position.

Objects changing positions with time with respect to the frame of reference are in motion while those which do not change position are at rest.

For example – A passenger sitting on a moving bus is at rest with respect to his co-passenger but at the same time, he is moving with the bus with respect to a person standing outside.