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.