History of US ZIP Codes: Used in 1963, changed to 9 digits in 1980

Postal Codes and Postal Code Maps

Zip codes are the zip code system used by the United States Postal Service (USPS) since 1936. The word ZIP is an acronym for Regional Improvement Program, correctly written in capital letters, and selected to indicate a more efficient delivery of mail.

So it's faster when the sender uses the code from the postal address. The basic format consists of five decimal digits. The extended ZIP+4 code, introduced in the 1980s, includes five digits for the zip code, a hyphen, and four digits that determine a more precise location than the zip code alone. The term ZIP code was originally registered as a service mark (a trademark) by the United States Postal Service, but its registration has expired.

ZIP codes specify only delivery points within the United States and its dependent countries, and the location of its armed forces. Postal codes are not reserved for mail destined for foreign destinations (except for U.S. military units stationed outside the United States). Therefore, international outbound mail should not include a postal code in the delivery address. The last line of a foreign address can only display the name of the destination country.