WordPress automatically saves your post (or page) while you are editing it. This is called WordPress auto-draft. If you don’t hit the publish/update button, then the post/page will be saved as auto-draft and any modification to your post/page will not be visible in your public site. Over time, you could have multiple auto-drafts that you will never publish and hence you can clean them.
To clean WordPress auto-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 = 'auto-draft'