MOTION

• Motion is relativistic process that means if a body is in motion for another body that doesn't means the body is in motion for all the body. 
• If a body is in motion for you it doesn't means it is in motion for all.
• A body is said to be in motion for you if that body is continuously changing its distance from you with respect to time.

For example:-

If two persons are sit in car and you are standing on road. Both the person that sit in car is in motion for you but in rest for each other.