Here's a breakdown:

* Ball: This refers to the 3-dimensional object, like a basketball or a tennis ball.

* Sphere: This is the mathematical term for the shape of the ball's surface. It's defined as the set of all points in space that are a fixed distance (the radius) away from a central point.

Think of it this way: if you cut a ball in half, the curved surface of that half is a hemisphere. The entire surface of the ball is a sphere.