What Are The "Pre-Stamped" Envelopes Called?

Hi,
The other day I realized that my Scott National albums don't have spaces for the pre-printed stamps that are found on envelopes and postcards. The ones I'm familiar with are from the mid 20th century, but I can't recall their proper name.

Obviously these are collected, but I wonder why the National doesn't have spaces for them...........

Your input would be appreciated!

Thank you - for this - and for all my other pesky questions.

Postal stationery is back of the book stuff. The envelopes use a "U" prefix and the postal cards use a "UX" prefix.

The "stamp" part of postal stationery is called an indicium. The envelopes are called stamped envelopes and sometimes postal envelopes. What looks like a postcard is called a postal card. Many stamp albums don't have spaces for postal stationery or if they do, it's just for cut squares of the indiciums from stamped envelopes. You can always make your own album pages as well.