Origin: Latin prefix post-
Postage has 3 different meanings across 1 category:
the charge for mailing something
"I need to pay the extra postage because I decided to send a heavier package than planned."
a small adhesive token stuck on a letter or package to indicate that that postal fees have been paid
"I forgot to stick the postage on my envelope before dropping it in the mailbox, so the clerk told me I'd need to pay for it at the counter."
The charge for posting an item.
"I need to pay five dollars in postage before I can mail my birthday card."
In plain English: Postage is the money you pay to send a letter or package through the mail.
"I need to buy some stamps because I ran out of postage for my letter."
Usage: Postage refers specifically to the money you pay to send mail or packages through the postal service. It is incorrect to use this term when referring to the physical stamps themselves or the act of mailing something.
The word postage comes from combining the root post with the suffix -age. It originally referred to charges related to sending mail by post and entered English as a straightforward compound of these two elements.