While all affixed postage stamps and other markings applied to mail to qualify it for postal service is franking, not all types and methods are used to frank all types or classes of mails.
"Postage" franking is the physical application and presence of postage stamps, or any other markings recognized and accepted by the postal system or systems providing service, which indicate the payment of sufficient fees for the class of service which the item of mail is to be or had been afforded.