means The internal framework of bones that supports and shapes a body, or by extension any bare supporting structure of a thing.

from From Greek 'skeleton', short for 'skeleton soma' meaning 'dried-up body' — the neuter of 'skeletos', 'dried up, withered', from the verb 'skellein', 'to dry out'. So a skeleton is literally what's left when everything moist and living has gone: the body desiccated down to its frame. It entered English in the late 1500s, and from the bones outward the word spread to anything stripped to its essentials — a skeleton crew, the skeleton of a plan.