This is our top-level category; looking at it another way, it is the root category.
Ideally, every other category should be a subcategory of at least one other, and every article should be in at least one category; many will fit well into two or more (e.g. location, year, and subject-matter).
To add a new category to a page you can click the Category button at the bottom of the page and type in the name you'd like your category to be called (for Wikia theme). Another way to add a new category to a page, just add
[[Category:Categoryname]] to the end of the article or existing category page (for MonoBook theme).
A full list of existing categories can be found at Special:Categories.
This category has the following 4 subcategories, out of 4 total.