an official mark stamped on letters and other mail, serving as a cancellation of the postage stamp and indicating the place, date, and sometimes time of sending or receipt.
post·mark (pōst'märk') n. An official mark printed over a postage stamp, especially one that cancels the stamp and records the date and place of mailing. tr.v.
post·marked, post·mark·ing, post·marks To stamp with such a mark.