To register post metadata, use register_post_meta( $post_type, $meta_key, $args ).
To register term metadata, use register_term_meta( $taxonomy, $meta_key, $args ).
To register post metadata, use register_post_meta( $post_type, $meta_key, $args ).
To register term metadata, use register_term_meta( $taxonomy, $meta_key, $args ).