Use the adjective skeletal to describe anything that relates to a skeleton or anything without a lot of "flesh," like the skeletal remains of a bird or the skeletal outline of a paper that is missing all the details.
If you're a scientist or a doctor, you may use the word skeletal mostly to talk about skeletons, but it also describes someone who is dangerously thin. A skeletal stray dog has probably been living on the streets for a long time. This word is also used figuratively to describe something that has not yet been "fleshed out" — like a skeletal staff or crew that operates without a lot of support. The root of skeletal is the Greek skeleton, "dried-up body, mummy, or skeleton."