WordPress at a glance
action is not described

woocommerce_product_on_backorder action-hook . WC 1.0

Usage

add_action( 'woocommerce_product_on_backorder', 'action_function_name_9172' );
function action_function_name_9172( $array ){
	// action...
}
$array
-

Where the hook is called

wc_trigger_stock_change_notifications()
woocommerce_product_on_backorder
woocommerce/includes/wc-stock-functions.php 237-244
do_action(
	'woocommerce_product_on_backorder',
	array(
		'product'  => wc_get_product( $change['product']->get_id() ),
		'order_id' => $order->get_id(),
		'quantity' => abs( $change['from'] - $change['to'] ),
	)
);

Where in WP core the hook is used WooCommerce

Usage not found.