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.

Nowadays, people don't send letters to one another when they want to catch up. You may get holiday or birthday cards from your parents, grandparents or other family members and friends, but for the ...

Today marks the 50th anniversary of the Zone Improvement Plan, the network of ZIP codes we use for everything from mail delivery to credit card security. The U.S. Postal Service began using the ...