In
philately, a
cachet is a printed or stamped design or inscription, other than a
cancellation or pre-printed postage, on an
envelope,
postcard, or
postal card to commemorate a postal or philatelic event. There are official and private (independent of postal authorities) cachets. They commemorate everything from the first flight on a particular route, to the
Super Bowl. Cachets are also frequently made, either by private companies or a government, for
first day of issue stamp events or "second-day" stamp events. They are often present on
event covers.