When we send letters, we write 'zip code' on the envelope. What is the meaning of 'zip'? Why is 'zip' used here?

The word "zip" is an acronym for Zone Improvement Plan.

https://en.wikipedia.org/wiki/ZIP_Code

Zip codes are 5 (or 9) numbers after the name of the state. For instance, my address ends with MI 49008.

The term "ZIP" is an abbreviation for "Zone Improvement Plan." The ZIP code system was introduced by the United States Postal Service (USPS) in 1963 to improve mail sorting and delivery efficiency.

ZIP codes are a numerical code assigned to specific geographic regions within the United States. Each code represents a particular area, such as a city, town, or specific group of addresses. By using ZIP codes, the USPS can easily identify the destination of a letter or package and sort it accordingly for efficient transportation and delivery.

The term "zip" itself is a play on words, suggesting that mail should move quickly and smoothly through the postal system. It became a popular and easily recognizable term for the postal code system. So, when we write "zip code" on an envelope, we are indicating the specific numerical code that corresponds to the recipient's location, ensuring correct sorting and prompt delivery.