Answer;
Internal layer of spongy bone in flat bones.
The term diploe refers to the internal layer of spongy bone in flat bones.
Explanation;
Diploe is the soft material that is between the hard and the outer walls of the bones of the cranium.
It is the endosteum (delicate connective tissue that covers the trabeculae and canal of the spongy bone) covered trabeculae of a spony bone.
Diploe is found in short, irregular, and flat bones.