For questions about designing adversarial monsters and NPCs for use in a game.
Monster design is about creating monsters (i.e. adversarial NPCs) for use in a game.
Monster design is distinct from encounter-design in that monster design is traditionally encounter-agnostic. In contrast, character-creation focuses on creating player characters, whereas game-design is about the design of the overall system.
Monster design is probably not the best tag when asking questions about monster creation at the world-building scope; for that, use setting or campaign-development.