What is "zip code"

zip 4 \zip + 4\ (z[i^]p" pl[u^]s f[=o]r`), n. a full nine-digit zip code. See zip code.

zip code \zip" code`\ (z[i^]p"k[=o]d`), n. [zone improvement plan.] any one of a set of numbers assigned by the United States Postal Service to designate a particular postal delivery area. One or more zip codes are assigned to each post office. The numbers initially had five digits (the initial code), indicating state and post office. Later, four more optional digits were added (the expanded code) indicating the box number or delivery route. The full set of nine digits is also referred to as zip + 4. The code is appended in an address to the line bearing the city and state names, as in ``Plainfield, NJ 07062''. [Also spelled ZIP code and Zip code.]

n. (context chiefly US English) A postal code, especially for addresses served by the US Postal Service, consisting of a five- or nine-figure number.

n. a code of letters and digits added to a postal address to aid in the sorting of mail [syn: postcode, postal code]

ZIP Codes are a system of postal codes used by the United States Postal Service (USPS) since 1963. The term ZIP, an acronym for Zone Improvement Plan, was chosen to suggest that the mail travels more efficiently, and therefore more quickly (zipping along), when senders use the code in the postal address. The basic format consists of five decimal numerical digits. An extended ZIP+4 code, introduced in 1983, includes the five digits of the ZIP Code, a hyphen, and four additional digits that determine a more specific location within a given ZIP Code. The USPS provides a free online lookup tool for ZIP Codes.

The term ZIP Code was originally registered as a servicemark (a type of trademark) by the U.S. Postal Service, but its registration has since expired. USPS style for ZIP is all caps and the "c" in code is also capitalized, although style sheets for some publications use sentence case or lowercase.