When a post is created in WordPress, items like title, content, ID and status are stored in the wp_posts table. However that’s not the only place where WordPress stores post information. There also exists a wp_postmeta table that contains all the extra bits. Each extra bit is stored against a meta key. This meta key is used for retrieval and updating.

WordPress not only uses wp_postmeta internally, but also encourages plugins and themes to use it as a way of storing extra data for posts. Hundreds of premium and free plugin use the post meta table. Frontend Publishing Pro allows you create generic custom fields based on meta keys.