The skull is composed of both the facial bones and the cranium. The cranium is the top part of your skull: the frontal bone, parietal bones, temporal, and occipital bone. They have a similarity in their function, in that they protect the head. But they protect different parts of the head. The cranium protects the brain, the top of the head. And the rest of the skull protects the rest of the head and the face.

A skull is your whole head bone. The cranium is the upper part that does not move. It does not include the "mandible" - the lower part of your jaw (mouth), which moves.