A tip (also called a gratuity) is a sum of money customarily tendered to certain service sector workers for a service performed or anticipated. Tipping and the amount are a matter of social custom and social practices vary between countries and settings. In some locations tipping is discouraged and considered insulting and in some locations tipping is expected from customers. The customary tip can be a specific range of monetary amounts or a given percentage of the bill. In some circumstances, such as with U.S. government workers, receiving of tips is illegal. A service charge is sometimes added to bills in restaurants and similar establishments. Tipping may not be expected when a fee is explicitly charged for the service.