This is our "top-level" category.
Every other category and every article should be in at least one category. (Any articles that are not can be found at Special:uncategorizedpages.) Many should be in two or more, eg a geographical region and a subject-matter category.
For principles of maximising usefulness and minimising illogicalities with categories, see project:categorisation.
Pages that are not articles (eg, pages in the Help or Template namespaces) may be in a category if there is value in reaching them quickly from other pages.
This category has the following 5 subcategories, out of 5 total.