The main entity within Wordpress are users, posts and their comments, categories, tags, options, and links.
|Meta data, comment features information
|The comments of posts
|links entered into the Links feature of WordPress (deprecated, but can be re-enabled with the Links Manager plugin)
|The Options set under the Admin > Settings panel
|Meta data, post features information. Some plugins may add their own info to this table.
|Posts, pages and navigation menu items
|The categories for both posts and links and the tags for posts
|Meta data, term features information
|Association between posts, categories, tags, links from the wp_terms table
|Taxonomy of category, link, or tag
|Meta data, user features information
Official link: https://codex.wordpress.org/Database_Description