The book's introduction, written by the author, has an explanation of the title. In it he writes the following explanation for the title. He says that the title refers to a person who
has the appearance of an organism lovely with colour and juice but is in fact only a clockwork toy to be wound up by God or the Devil or (since this is increasingly replacing both) the Almighty State.
Basically, what the title is talking about is a person that behaves like a programmed toy or machine. The person has a mechanical set of morals and is essentially a robot, yet the person is in fact an actual biological creature. The story itself shows this concept through what happens to Alex. He is a character that for all intents and purposes has no moral reservations about anything. He rapes a ten year old, for example. He then goes through a behavioral brainwashing procedure that causes him to be sick at the mere thought of violence. This changes his entire behavior pattern, and he is essentially a reformed member of society. Unfortunately, his behaviors are not his. Alex has been programmed to behave that way. He essentially is acting the part of a robot despite the fact that he is a human organism.