A category is one of the default taxonomies in WordPress. It is used to sort and group content into different sections.
For example, a news site publishing content on a variety of topics may divide the site into sections using the following categories: Politics, Sports, Culture, Weather, and so on.
Categories can be added, edited, organized and removed from the menu Posts > Categories.
If you do not define a category, the post will automatically be placed in the default category. It is not possible to remove the default category. If you want to change it, you can do so in the menu Settings > Writing. You will need to designate another category that you have created beforehand to replace the “Uncategorized” category that was automatically set by WordPress.
Deleting a category will not delete the posts in it. These posts will automatically be added to the default category.
If your theme allows it, categories can be displayed in a sidebar using the “Categories” widget via the Appearance > Widgets menu. This will list all categories, except those where there are no posts.
Categories can be hierarchical. This means that you can create parent and child categories. A parent category lists all the items in a child category.
For example, a news site may have a parent category “News”, which will group the child categories “Local”, “National”, “International”.