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.

Like our social security numbers, birth dates, and phone numbers, our ZIP codes are one of many seemingly random number sequences etched in our minds. But, for the most part, the only people who know ...

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 ...