Meta boxes in WordPress are the draggable boxes that exist in WordPress admin. It contains form fields to set information about the post, page, custom post type, terms, users, comments etc.
Meta box can also be used to display information like in the WordPress dashboard. By default, WordPress comes with some metaboxes that exist in the edit screen of a post or page as shown in the below image. Eg: editor, featured image, post format, category, template etc.