The additional pieces of data that attached to a post its a Metadata in WordPress. Let’s suppose, you have products and your products custom post type might need a price stored with each Product entered in your site. This price can be stored as metadata and it easily displayed on the Product detail page. In WordPress terminology post metadata is often referred to as Custom Fields. In the admin dashboard of WordPress this is a more user-friendly term. On the post-editing screen WordPress adds a Custom Fields meta box by default. As shown in Figure below.
In WordPress for the supports argument if a custom post type has the custom-fields value defined, this meta box will also appear. The metadata of post are stored in the wp_postmeta table in your WordPress database.