This term, however, is relative. Your chair may actually be one of many seats on a speeding airplane. The important thing to remember here is that you are not moving in relation to your immediate surroundings. If rest were defined as a total absence of motion, it would not exist in nature. Even if you were sitting in your chair at home, you would still be moving because your chair is actually sitting on the surface of a spinning planet that is orbiting a star, and the star is moving through a rotating galaxy that is, itself, moving through the universe.
Motion is also a relative term.
All matter in the universe is moving all the time, but in the first law, motion means changing position in relation to immediate surroundings. A ball is at rest if it is sitting on the ground. The ball is in motion if it is because then it is changing its position in relation to its surroundings. A rocket blasting off the launch pad changes from a state of rest to a state of motion. The third term important to understanding this law is unbalanced force.