An organism that is partly mechanical and partly biological is a cyborg. The Star Wars character Darth Vader is a good example of a cyborg: he's a person whose body has been improved through technology. He's mainly, but not entirely, human.
The term cyborg was coined in 1960, from cybernetic and organism, and since then it's mainly been used in fiction and as a theoretical concept. The meaning of this word has changed over time as science fiction ideas (from virtual reality to artificial heart valves) increasingly become real. Some people think that individuals using any kind of internal medical device, from pacemakers to cochlear implants, could technically be classified as cyborgs.