When an object is at rest, it means it is not moving. Therefore, the speed of an object at rest is zero. Speed is defined as the rate at which an object covers distance, so if the object is not covering any distance, its speed is zero.
On the other hand, if an object is moving with a constant velocity, its speed remains constant over time. Velocity is a vector quantity that includes both speed and direction. If the velocity is constant, it means the object is moving at a steady speed in a particular direction. In this case, the speed of the object will be equal to the magnitude of its velocity.