In philately, a cachet's 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're official and private 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're often pres… (More on Cachet)