n (anatomy) The system that provides support to an organism, internal and made up of bones and cartilage in vertebrates, external in some other animals.
n A frame that provides support to a building or other construction.
n (figuratively) A very thin person.
n (From the sled used, which originally was a bare frame, like a skeleton.) A type of tobogganing in which competitors lie face down, and descend head first (compare luge). See Wikipedia:Skeleton (sport)
n (computing) A client-helper procedure that communicates with a stub.