The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Magnifying glasses (1 member)
- Magnifying glasses in art (1 member)
- Main message boxes (17 members)
- Main topics (2 members)
- Maintenance data structures (3 members)
- Mammalia taxa by rank (1 member)
- Mammals by adaptation (1 member)
- Marine animals (1 member)
- Marine mammals (1 member)
- Marker templates (1 member)
- MediaWiki software tracking categories (4 members)
- Meta categories (1 member)
- Metacategories not fully sorted into flat categories (1 member)
- Metaphysics (1 member)
- Microsoft video games (1 member)
- Minecraft (0 members)
- Miocene first appearances (1 member)
- Models by type (1 member)
- Mojang Studios (1 member)
- Mollusca (0 members)
- Multi-template documentation (1 member)
- Multimedia icons (1 member)
- Musicians by name (1 member)
- Navigation by country templates (1 member)
- Navigational boxes without horizontal lists (1 member)
- Navigational templates (1 member)
- Neomura (1 member)
- Nihon Ken (1 member)
- Nintendo (1 member)
- Nintendo 3DS games by name (1 member)
- Nintendo 64 (1 member)
- Nintendo Switch games by name (2 members)
- Nintendo consoles (2 members)
- Nintendo hardware (1 member)
- Noindexed pages (2 members)
- Non-sporting breeds (1 member)
- Number 64 on objects (1 member)
- Nuvola 2.0+ icons (1 member)
- Nuvola 2.0+ icons needing conversion to SVG (0 members)
- Nuvola PNG icons (1 member)
- Nuvola icons (1 member)
- Observation (1 member)
- One-letter templates (1 member)
- Online games (1 member)
- Open-world video games by name (1 member)
- OpenGL (1 member)
- Optical device icons (1 member)
- Orders of Mammalia (1 member)
- Orders of Synapsida (1 member)
- Otariidae (1 member)