How I could add a new label in post page

Hello,

I was wondering how I could do like on the picture. Because I have looked at the code and am not sure about how to do that.

Because page are generaly declared like this if I m right but don t what I m allowed to do to make my modification :

$labels = array(
'name' => __( '', '', ),
'singular_name' => __( '', ),
'search_items' => __( '', ),
'all_items' => __( '', ),
'parent_item' => __( '', ),
'edit_item' => __( '', ),
'update_item' => __( '', ),
'add_new_item' => __( '', ),
'menu_name' => __( '', )
);