Here's the summary for the wikipedia article you mentioned in your comment:

A ZIP Code is a system of postal codes used by the United States Postal Service (USPS). Introduced on July 1, 1963, the basic format consisted of five digits. In 1983, an extended ZIP+4 code was introduced; it included the five digits of the ZIP Code, followed by a hyphen and four digits that designated a more specific location. The term ZIP is an acronym for Zone Improvement Plan; it was chosen to suggest that the mail travels more efficiently and quickly (zipping along) when senders use the code in the postal address. ZIP Code is a trademark and ZIP+4 is a registered trademark of the United States Postal Service, which also registered ZIP Code as a service mark until 1997.

^article^ ^|^ ^about^