Difference between rest and motion:

Rest:

          A body is said to be at rest if it does not change its position concerning its surroundings.

Motion:

          A body is said to be in motion if it changes its position concerning its surroundings.

The state of rest or motion of a body is relative. For example, a passenger sitting in a moving bus is at rest because he/she is not changing his/her position concerning other passengers or objects on the bus. But to an observer outside the bus, the passengers and the objects inside the bus are in motion.