What is Zip Code?

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 basic format consists of five digits. There are no ZIP codes reserved for designating mail bound for foreign destinations (with the exception of U.S. military units stationed outside of the United States), and therefore, international outbound mail should not include a ZIP code in the delivery address.

In order to promote the idea of ZIP codes, Mr. Zip” appeared as the cartoon mascot for the campaign, touting Put ZIP in your mail!” While Mr. Zip is obviously a fictional figure, a Philadelphia postal inspector named Robert Moon is widely considered to be the real-life version and the father of the ZIP code even though the Postal Service refused to give him sole credit for the invention.

Like area codes , ZIP codes are sometimes divided and changed, especially when a rural area becomes suburban Typically, the new codes become effective once announced, and a grace period (e.g., one year) is provided in which the new and old codes are used concurrently so that postal patrons in the affected area can notify correspondents, order new stationery, etc.

Reference : USPS