A tip (also called a gratuity) is a sum of money tendered to certain service sector workers for a service performed or anticipated. Such payments and their size are a matter of social custom. Tipping varies among cultures and by service industry. Though a tip is seldom required, and its amount is usually at the discretion of the patron being served, in some circumstances failing to give an adequate tip when one is expected is a serious faux pas, and may be considered very miserly, a violation of etiquette, or unethical. In some other cultures or situations, giving a tip is not expected and offering one would be considered at best odd and at worst condescending or demeaning. In some circumstances, such as with U.S. government workers, receiving of tips is illegal.