A skeleton was the support structure for an animal. There were two kinds: an exoskeleton, which was external, or an endoskeleton, which was internal.
The haunted house in the Festival of Ghana had a skeleton which dropped from the ceiling, frightening Barbara and Vicki. (TV: "Journey into Terror")
Some Gelth possessed several skeletons in the crypt of Cheltnam Abbey, then tried to open the Cardiff Rift permanently. They were stopped by the Tenth Doctor. (PROSE: Scared Stiff)
When Death entered the prime universe after someone was resurrected with the left-handed resurrection gauntlet, it had the physical form of a human skeleton shrouded in dark grey vapour. (TV: Dead Man Walking)
Gulfrargs were one of the few sentient species that evolved without a skeleton or an epidermis. (AUDIO: The Extinction Event)