Franking (or "franks") are any and all devices or markings such as postage stamps (including those pre-printed on postal stationery), printed or stamped impressions, codings, labels, manuscript writings (including "privilege" signatures), and/or any other authorized form of markings affixed or applied to mails to qualify them to be postally serviced.

While all affixed postage stamps and other markings applied to mail to qualify it for postal service are franking (or "franks"), not all types and methods are used to frank all types or classes of mails. Each of the world's national postal administrations establishes and regulates the specific methods and standards of franking as they apply to domestic operations within their own postal systems. Although there are differences in the manner that the postal systems of the 191 nations that belong to the Universal Postal Union (UPU) apply and regulate the way their mails are franked, most mails fall under one (and sometimes more) of four major types and/or methods of franking: postage (stamps, etc.), privilege, official business, and business reply mail.