A metabox in WordPress is a user-friendly interface that allows you to easily add flexible fields without altering the system’s core tables. This additional data is grouped and displayed on a content editing page, whether it’s a post, a page, etc.

Metaboxes in WordPress work by using specific database tables such as wp_posts, wp_terms, wp_users, and wp_comments to store essential information like the post title, categories, and publication date. For additional metadata, WordPress has separate tables such as wp_postmeta, wp_termmeta, wp_usermeta, and wp_commentmeta, allowing you to add custom fields as key/value pairs.

Metaboxes facilitate the display and bulk editing of this metadata on editing pages. Typically, the keys correspond to the names of the custom fields, while the values ​​represent their content. Each metadata element is associated with a specific entity (article, term, user, comment) through its respective ID, which is stored as a key.

To create metaboxes, there are dedicated online tools that greatly simplify the process. These can also be called meta boxes, or metaboxes in the plural.