US ZIP codes are a type of postal code used within the United States to help the United States Postal Service (USPS) route mail more efficiently. Some still refer to ZIP codes as US postal codes.
The term ZIP stands for Zone Improvement Plan. The basic 5-digit format was first introduced in 1963 and later extended to add an additional 4 digits after a dash to form a ZIP+4 code.
The additional 4 digits help USPS more precisely group mail for delivery. Though ZIP codes were originally developed for USPS, many other shipping companies such as United Parcel Service (UPS), Federal Express (FedEx), DHL, and others make use of ZIP codes for sorting packages and calculating the time and cost of shipping a package (the shipping rate).
Types of Zip Codes
- Unique/single high volume address (ex. 20505 for the CIA in Washington, DC)
- PO Box only (ex. 22313 for the PO Boxes of Alexandria, VA)
- Military
- Standard (all other ZIP codes)
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