Describe the difference between average speed and constant speed

Average speed deals with "change" in displacement of a body with time while constant speed deals with "constant" displacement of a body within a specific time.

Explanation:

Average speed is defined as the change in displacement of a body in a specific time interval while constant speed occurs when a body covers a particular distance within a varying time but the displacement of the body is constant.

In average speed, the displacement changes with respect to time but for constant speed, the displacement of the object doesn't change but distance is covered at a particular time.