WordPress at a glance
action is not described

comment_(old_status)_to_(new_status) action-hook . WP 2.7.0

Fires when the comment status is in transition from one specific status to another.

The dynamic portions of the hook name, $old_status, and $new_status, refer to the old and new comment statuses, respectively.

Usage

add_action( 'comment_(old_status)_to_(new_status)', 'action_function_name_2854' );
function action_function_name_2854( $comment ){
	// action...
}
$comment(WP_Comment)
Comment object.

Where the hook is called

wp_transition_comment_status()
comment_(old_status)_to_(new_status)
wp-includes/comment.php 1626
do_action( "comment_{$old_status}_to_{$new_status}", $comment );

Where the hook is used (in WP core)

Does not used.