Motion is the distance one object moves

That seems easy enough, except for one fact. Everything is moving.  You may seem to be sitting still
in front of your computer, but both you and your computer is moving through space.

So before you can measure how far something moves you have to establish a
reference point.
Are the stairs moving under the
motorcycle, or is the motorcycle
moving over the stairs?

The answer depends upon your
reference point.
The reference point is the thing
that you measure motion

You may want to think of it as
the thing that is standing still.
Chapter 12 - Motion - The Reference Point
If we use the car as a reference point, the plane seems
to be moving backwards.  But, if we use the screen
(you) as a reference point they are both moving the
same direction but the car is moving faster.

(please don't ask why the car is going faster than the
jet, it just is!)