Categories: “Each post in WordPress is filed under a category. Thoughtful categorization allows posts to be grouped with others of similar content and aids in the navigation of a site.”
About WordPress Categories
Categories are an essential part of WordPress. They help group like topics and posts together, which makes it easier for people to search by topics that interest or pertain to them. Categories are not to be confused with tags. Categories tend to be based on broader topic points than the tags that people enter for their posts.
Categories can be placed in a number of different places, depending on what themes and widgets you are working with. They can be displayed at the top of a post, the bottom of a post, on the menu, in the sidebar or in individual post view.
According to the support site for WordPress.com:
“Your posts will appear in the topics listings of any tags or categories you use. Therefore, assigning tags and categories to your post increases the chance that other WordPress.com users will see your content.”
The number of tags and categories that can be applied to a post on a public topic listing are limited between 5 and 15 total. That’s tags and categories combined. Selecting a large number of categories limits the chances of your post being selected for inclusion in the topic listings.