The tin man was a character from the 1939 movie The Wizard of Oz.
History and specifics[]
During the Vagra II mission in 2364, Armus called Data a "tin man". (TNG episode: "Skin of Evil")
"Tin Man" was also the codename assigned to the Gomtuu entity by Starfleet in 2366, prior to learning its true name. (TNG episode: "Tin Man")