What do the Z, I, and P in “ZIP code” stand for? And what do the numbers represent?

It’s a hectic time of year for the U.S. Postal Service. Those packages you ordered on Cyber Monday are steadily arriving. You’re probably even receiving a few holiday greetings the old-fashioned way — snail mail.

The half million employees who work for the USPS rely heavily on the five- or nine-digit ZIP codes for efficient and reliable mail delivery. So, it makes sense that the term “ZIP code” would be related to being zippy, which means “lively” or “peppy.”

“ZIP” is actually an acronym for Zone Improvement Plan. However, the USPS intentionally chose the acronym to indicate that mail travels more quickly when senders mark the postal code on their packages and envelopes.

The general system of ZIP codes used today was implemented in 1963. Prior to this system, the USPS used a system of postal zones, which was only applicable to large cities. This is where the “improvement” part comes into play.

The basic ZIP code has five digits. The first three digits refer to a sectional center facility (or SCF), what is basically a network of super post offices. All of the post offices that have those three digits in their ZIP code have their mail sorted and processed by the same SCF.  The last two numbers designate the specific post office within an SCF’s territory.

In the 1980s a new system was introduced called ZIP+4. Four additional digits (with a hyphen) were added to the basic code. This allowed senders to indicate an even more precise location, such as a particular block or apartment building. The rise in post office boxes also made this greater level of precision necessary.

Here’s one more postal term to file away: Postnet. The Postnet is a ZIP code translated into a barcode and printed on a piece of mail. The Postnet makes it more efficient for automated machines to sort mail.

Now that you have command of the ZIP code, try the challenge of understanding how to read a barcode. Be warned; it’s not easy. Here’s our explanation.