1. A person only capable of grinding out code, but unable to perform the higher-primate tasks of software architecture, analysis, and design. Mildly insulting. Often applied to the most junior people on a programming team.
2. Anyone who writes code for a living; a programmer.
3. A self-deprecating way of denying responsibility for a management decision, or of complaining about having to live with such decisions. As in "Don't ask me why we need to write a compiler in COBOL, I'm just a code monkey."