woocommerce_order_item_product │ filter-hook │ WC 1.0

Usage

add_filter( 'woocommerce_order_item_product', 'wp_kama_woocommerce_order_item_product_filter', 10, 2 );

/**
 * Function for `woocommerce_order_item_product` filter-hook.
 * 
 * @param  $product 
 * @param  $that    
 *
 * @return 
 */
function wp_kama_woocommerce_order_item_product_filter( $product, $that ){

	// filter...
	return $product;
}

$product

-

$that

-

Where the hook is called

return apply_filters( 'woocommerce_order_item_product', $product, $this );

Where the hook is used in WooCommerce