the impression made by the post office on a cover indicating the time and place of mailing. Postmarks may be made by machine or handstamp. Postmarks are most commonly circular, but are also found as ovals, boxes, straight lines and spray ons. Postmarks are not cancels, although they are sometimes used for that purpose, and the two terms are often and incorrectly used interchangeably.
Any mark, handstruck, machine-applied or in manuscript form, used on postal items in order items in order to cancel the stamps and/or record the date and origin of their transit through the mail services. (see Cancellation).