A decimal number that (a) is assigned to each U.S. Postal Service office in the United States, (b) is used to expedite the transfer, delivery, and forwarding of mail, (c) is equivalent to the address designators, address-indicating groups, or destination addresses-indicating groups, or destination addresses that are used on messages for electrical transmission, (d) currently consists of five (5) essential decimal-digit numerals plus four (4) digits for local destinations. Note 1: Street names, house numbers, box numbers, and addressee names are significant for local mail delivery, however the city and town names and the state codes, though helpful, are redundant when the proper ZIP code is given. Note 2: Foreign countries have also adopted a form of ZIP-code addressing. Note 3: It is essential that the ZIP code be legibly and accurately cited on all Postal Service domestic and foreign mail. See also  accuracy,  address designator,  addressee,  address-indicating group,  code,  decimal digit,  destination address,  electric,  electronic mail,  message,  name,  number,  numeral,  post,  postal address,  redundancy,  transfer,  transmission.