This is an information page.
It is not one of Wikipedia's policies or guidelines, but rather intends to describe some aspect(s) of Wikipedia's norms, customs, technicalities, or practices. It may reflect varying levels of consensus and vetting.
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.
Categories are not displayed in the mobile version. Mobile users can click "Desktop" at the bottom of a page to see the desktop version with categories. Registered users can enable Advanced mode which includes a "Categories" button.
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:
Category:Main topic classifications ↓ Category:History ↓ Category:History by location ↓ Category:History by country ↓ Category:History of Australia ↓ Category:History of Australia by location ↓ Category:History of Australia by state or territory ↓ New South Wales, Queensland, etc.
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.