Your billing zip code, or credit card postal code, is the five-digit number on the bottom right, which in this sample is 90210. This would be the zip code associated with your billing address.

Learn the history and meaning of usps postal codes, why it's called a ZIP code, whether a postal code is a ZIP code, and what ZIP code numbers stand for.

Here's what to know on how to address an envelope, write a return address, find a zip code, send letters internationally and figure out which stamps are best.