This used to be called a fuel surcharge, but the DOT released guidance that said that fuel surcharges must accurately reflect the incremental fuel cost to transport a passenger on the flight above some reasonable baseline. In response, UA renamed it an "international surcharge".

The reality is that it is just part of the cost of the ticket with and in practice is barely different than if the base fare was just $500 more (except that it is generally consistent for a given route regardless of class of service, as well as usually non-discountable and non-commissionable).