What's is meant by relative motion?

Relative motion means a motion relative to a reference point. We can also say, relative motion means motion referred or observed from a reference point.

For example, Alex is in a train and Ace is at the station, when the train starts moving, for Ace it is moving at a speed of 10 m/s, but for Alex it is moving at 0 m/s, or we can say that it is at rest for Alex, but in motion for Ace. This is relative motion.

relative motion is the motion of an object compared to that of another object.for example two cars driving in the same highway in the same direction.

I hope this helps