A body is said to be in motion if it changes its with respect to the surroundings.

Hint:A body can be either in motion or in rest. Motion can only be recognised if analysed with respect to some reference point. For a body to move, the distance of the body from a reference point must keep changing with respect to time.

Complete step by step solution:
We know, a body is said to be in motion, when it has covered a distance. The parameter “distance covered “is measured in terms of the change in position of the body.
Therefore, when a body moves, there must be a change in its position with respect to the surroundings.
We found a word Displacement, this means that a body in motion will reach a new place, than its previous location, this change in position occurs due to the displacement of the body.

Additional information:
Motion of a body is determined by factors such as:
Distance travelled by the body
Displacement occurred in the body
Velocity of the body
Acceleration of the body.
Distance and displacement are parameters that indicate the path taken by the body, however displacement is basically the shortest path that can be taken by the both to reach one location from another.
Whereas, displacement refers to the longest path taken.
We know, velocity is the rate of change of position of a body with respect to a frame of reference.
Here, the frame of reference, can be anything, for example, ground, any other moving body and many more.
Acceleration indicates the rate of change of velocity of the moving body.

Note:
Distance is a scalar quantity, having only magnitude.
Displacement is a vector quantity having both magnitude and direction.
Both velocity and speed indicate change of position of the body, but , speed is a scalar quantity and velocity is a vector quantity.