WordPress allows you to save a post or a page without having to publish it immediately. This way you can work on it as much as you want and publish it only when it is ready. This is called a WordPress draft. Over time, you could have multiple drafts that you will never publish and hence you can clean them.
To clean these drafts, you can either use our plugin Advanced Database Cleaner or execute the following SQL code (which is used by the plugin) directly via your phpMyAdmin:
DELETE FROM posts WHERE post_status = 'draft'