What do the letters “ZIP” stand for in the United States postal code?

A ZIP Code is a postal code used by the United States Postal Service (USPS). Introduced in 1963, the basic format consists of five digits. In 1983, an extended ZIP+4 code was introduced; it includes the five digits of the ZIP Code, followed by a hyphen and four digits that designate 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 servicemark by the USPS, but its registration expired in 1997.

The early history and context of postal codes began with postal district/zone numbers. The United States Post Office Department (USPOD) implemented postal zones for many large cities in 1943.

Robert Moon is considered the father of the ZIP Code; he submitted his proposal in 1944 while working as a postal inspector. The post office only credits Moon with the first three digits of the ZIP Code, which describe the sectional center facility (SCF) or "sec center". An SCF is a central mail processing facility with those three digits. The fourth and fifth digits, which give a more precise locale within the SCF, were proposed by Henry Bentley Hahn Sr.