WordPress at a glance
filter is not described

woocommerce_order_get_total_discount filter-hook . WC 1.0

Usage

add_filter( 'woocommerce_order_get_total_discount', 'filter_function_name_610', 10, 2 );
function filter_function_name_610( $NumberUtil::round, $that ){
	// filter...

	return $NumberUtil::round;
}
$NumberUtil::round
-
$that
-

Where the hook is called

WC_Abstract_Order::get_total_discount()
woocommerce_order_get_total_discount
woocommerce/includes/abstracts/abstract-wc-order.php 433
return apply_filters( 'woocommerce_order_get_total_discount', NumberUtil::round( $total_discount, WC_ROUNDING_PRECISION ), $this );

Where in WP core the hook is used WooCommerce

Usage not found.