Here's why:

* Velocity is a vector quantity, meaning it has both magnitude (speed) and direction.

* A body at rest has a velocity of zero. This means its speed is zero, and it's not moving in any direction.

* A body in motion has a non-zero velocity. It has a speed greater than zero and is moving in a specific direction.

Example:

* A car parked in a garage has a velocity of 0 m/s.

* A car driving down the road at 60 km/h has a velocity of 60 km/h eastward (assuming it's moving east).

Therefore, while both a body at rest and a body in motion can be described using the concept of velocity, their velocities are fundamentally different due to their different speeds and/or directions.