Most Americans know their ZIP code by heart. They type it into online forms, scribble it on envelopes and memorize it as part of their address. But not everyone knows the original meaning of the term.

ACCORDING TO THE UNITED STATES POSTAL SERVICE, - NO REFERENCE - TO "P.O. BOX," "BOX NO.," OR THE WORD "BOX" CAN or SHOULD BE MADE. The approved USPS designation is the number sign (#). The "W" in 60 W ...