Motion can be thought of as a change in position from a specific reference point. Motion is a relational measurement, which means that an object cannot be said to be "in motion" without having a reference point to which it is moving towards or away from. The most common reference points to motion are objects that appear to be stationary on Earth's surface.
When an object is in motion, it means that its position is changing. In other words, the distance of an object from another object is either becoming larger or becoming smaller. A reference point is a point that is considered stationary to which the object in motion can be related to. However, no object is truly stationary, so all motion is relative motion.
For instance, a chair that a person is sitting on is typically not said to be in motion, because it is not changing position in relation to the person sitting in it. However, if the reference point changes, then the chair does appear to be in motion. In reality, the chair is sitting on the surface of Earth, which is constantly spinning and rotating around the sun. Using the sun as a reference point means the chair that was assumed to be stationary is actually in motion.