What does ZIP mean?

What does the ZIP stand for in a postal ZIP Code?

http://www.m-w.com/ says:

Main Entry: zip code
Function: noun
Usage: often capitalized Z&I&P
Etymology: zone improvement plan
Date: 1963
: a number that identifies each postal delivery area in the U.S.

Holger

For a time before ZIP codes were introduced, there was a simpler system, that divided towns into zones, which you included in the address. For example, my parent's address was "Arlington 5, Virginia". The ZIP code system gave a unique number to each zone nationwide, for example, in the case of my parents, 22205. The later nine-digit expansion of the ZIP codes further subdivided the zones.

The use of "ZIP codes" was an advertising gimmick to get people to start using the new five-digit system (instead of the one digit zones that preceded them.)

Outside the US, these things are called simply "postal codes" which is much more reasonable.

What does the ZIP stand for in a postal ZIP Code?\

Zone Improvment Plan is of course the real answer, but we used to have a calendar at work that showed chimpanzees in various postal outfits, engaged in various work activities, and armed with postmark stampers.
The caption on one photo read: Zip code means we zip it back and forth across the country before delivery.
If you only knew,,,

[[For a time before ZIP codes were introduced, there was a simpler system, that divided towns into zones, which you included in the address. For example, my parent's address was "Arlington 5, Virginia". The ZIP code system gave a unique number to each zone nationwide, for example, in the case of my parents, 22205. The later nine-digit expansion of the ZIP codes further subdivided the zones. ]]

Hey! That's also *my* ZIP code!