WordPress at a glance
action is not described

unregistered_post_type action-hook . WP 4.5.0

Fires after a post type was unregistered.

Usage

add_action( 'unregistered_post_type', 'action_function_name_474' );
function action_function_name_474( $post_type ){
	// action...
}
$post_type(string)
Post type key.

Where the hook is called

unregister_post_type()
wp-includes/post.php 1317
do_action( 'unregistered_post_type', $post_type );

Where the hook is used (in WP core)

Does not used.