The Tin Woodman was a character from the Earth story The Wizard of Oz. He was a mechnical man who longed to be Human. His lamentation of not being Human was expressed in the tune If I Only Had a Heart. By the end of the story, he learned that he was always Human. He did not realize this as he worried so much. (TNG: "The Schizoid Man")
In the episode, Dr.Ira Graves referred to the Tin Woodman as a mechnical man. Another name for the Tin Woodman was Tin Man.