A ZIP Code is a postal code used by the United States Postal Service (USPS). Introduced in 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. The term ZIP Code was originally registered as a service mark by the USPS; its registration expired in 1997.