A category is a taxonomy that groups posts on similar topics. For example, you can assign your posts to categories, then display a list of categories in your blog’s sidebar. When a viewer clicks on a category, they will land at a category page that lists all of the posts belonging to that category.
WordPress administrators can choose to set a default category for new posts. If no default is set, they will appear as “Uncategorized.” You can add a post to an existing or new category in the Categories meta box that appears on the editing screen. You can also create a new category directly under Posts | Categories in the Administration Area.
You can nest categories under other categories. For example, you might create a “parent” category named music, and nest “child” categories for jazz, blues, rock, and folk within it.
Some sites choose to display introductory text on category pages, as well as post authors, publish dates, and last modified times. Others shorten category pages by displaying excerpts, rather than the full posts. You can change the design and behavior of category pages by tweaking your site’s themes and template files.
Site administrators can assign a unique color to each category through the Category Color plugin. For example, site owners may want to add brand or theme colors to the names, titles, backgrounds, and lines associated with categories.