Intelligent Mail barcode
The Intelligent Mail barcode is a bar code format for U.S. postal mailings, in the process of being deployed to supersede the older POSTNET codes.
Unlike other bar code systems which code based on bar thickness, Intelligent Mail bars (like POSTNET before it) are distinguished by their height. In POSTNET, there were two heights, while the Intelligent Mail format uses both height and vertical position to distinguish four different types of bars (known as a "four-state" system, transcribable using DAFT notation). Digits are encoded by combinations of these bar types. In addition to the encoding of zip codes as with POSTNET, additional digits identify service type and mailer (each bulk-mailing business gets its own identification number).
Bulk mailers apply bar codes to the pieces being mailed as one of the requirements of qualifying for discounted rates. The post office adds bar codes to other mail in the course of sorting.
The USPS can't seem to decide consistently whether to use its usps.com or usps.gov domain when providing resources related to these codes, as seen in the links below; this is in keeping with its split personality of being a company and a governmental entity at once.
Despite the "intelligent" nature of these codes, the high-IQ society Mensa has yet to gain the capacity to provide them on the mailing labels and address files sent to its local groups for mailing of their newsletters.