Meaning of “stamp” - Learner’s Dictionary

stamp

noun [ C ] uk us /stæmp/
PAPER (also postage stamp)

A2 a small, official piece of paper that you buy and stick onto a letter or parcel before you post it

MARK

a tool for putting a special ink mark on something, or the mark made by it:

a stamp in a passport
stamp of approval

official, public approval:

The president has put his stamp of approval on the proposal.

(Definition of “stamp noun” from the Cambridge Learner’s Dictionary © Cambridge University Press)