Categories are used in Wikipedia to link articles under a common topic and are found at the bottom of the article page. Clicking the category name displays a list of articles in that category, below a list of sub-categories (categories in that category) (if any). Categories allow readers to navigate through Wikipedia and find related articles.
All of the categories form a hierarchy, although sub-categories may be a member of more than one category. An example of a small part of this hierarchical structure looks somewhat like this:
The actual relationship is more complex since a category may appear as a subcategory of several other categories. The actual relationship of part of the category structure looks like this:
The uppermost category in the hierarchy is Category:Contents. From here all other categories branch out, including those that are used for the maintenance of Wikipedia.
If an entry in a category is shown in italics it is a redirect to an article of a different name or a section of an article that contains information about that particular subject.