Here's why:

* Velocity is a measure of both speed and direction.

* Rest implies an object is not moving, meaning it has no speed.

* Since velocity includes speed, an object at rest has a velocity of 0.

It's important to note that velocity is a vector quantity, meaning it has both magnitude (speed) and direction. While an object at rest has a speed of 0, it technically has a direction as well, though it's not usually specified.