A category is a WikiName that exploits WikiWiki's reverse linking: if you click on the title of a category page, you'll get a list of pages belonging to that category. To get a list of all categories, click the CategoryCategory title in the navigation area.
Here is a list of all pages containing the CategoryCategory wiki tag: <<FullSearchCached: execution failed  (see also the log)>>
To be consistent with the C2 category scheme, all categories start with the word "Category". For more information, see AboutCategoriesAndTopics.