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.

Esri also lets you look up monthly credit card charges per ZIP code or whether your neighborhood has a high percentage of "Financial Optimists" — people who plan to be better off than they are ...

There is also another type of postal code, the ZIP + 4 code. According to unitedstateszipcodes.org, the ZIP + 4 was established in 1983 and identifies an even more specific location within a ZIP code.