The skeleton or skeleton scaffolding constitutes the structural part of a body. It provides for stability and protection. If it is hidden beyond the surface it is called endoskeleton, otherwise exoskeleton.
The artificial design of skeletons is also known as skeleton crafting.
Slice skeletons (more commonly known as sliceforms) are made from slices. Those slices are frequently used in rapid prototyping since they can be quickly created using laser cutters. A typical example are the wing ribs of an airplane.
Beam skeletons are made of beams or stems. While artificial structures can clearly be classified into slice skeletons and beam skeletons, natural skeleton structures are often somewhere inbetween. Beam skeletons are found in radiolarians and various architectural tross constructions.
The core skeleton resides in the center of the body. It comprises some kind of spinal chord or medial axis to which other body parts are attached. Common examples are the bones in our limbs or the spar and ribs inside glider wings. Core skeletons are endoskeletons by definition.
The outer skeleton is hollow on the inside. So if the body is separated into layers, the outer skeleton is usually in the outermost layer of the body. A common examples is the human chest. Note that exoskeletons are always outer skeletons, but not vice versa.
We use the term grid skeleton or diaskeleton (from greek dia=through) to refer to skeletons made of bones that transcend the complete body. Grid skeletons are based on a grid shape intersecting the body.
While space-grid skeletons are derived from an external grid that doesn't take the body shape into account, body-grid skeletons are based on a coordinate system that is directly related to the shape of the body. Grid skeletons may be further classified into sliced grid skeletons and beam grid skeletons.
Skeletons can be skeletized again to create even more leightweight structures. Multilevel skeletonization is often used in large scale truss structres such as the Eiffel Tower but can also be observed in nature: vertebral bones are not made of a single piece – their spongy interior is a microskeleton in its own right.