39 U.S.C. § 3201: Definitions

As used in this chapter—(1) “penalty mail” means official mail, other than franked mail, which is authorized by law to be transmitted in the mail without prepayment of postage; (2) “penalty cover” means envelopes, wrappers, labels, or cards used to transmit penalty mail; (3) “frank” means the autographic or facsimile signature of persons authorized by sections 3210–3216 and 3218 of this title to transmit matter through the mail without prepayment of postage or other indicia contemplated by sections 733 and 907 of title 44; (4) “franked mail” means mail which is transmitted in the mail under a frank; (5) “Members of Congress” includes Senators, Representatives, Delegates, and Resident Commissioners; and (6) “missing child” has the meaning provided by section 403(1) of the Juvenile Justice and Delinquency Prevention Act of 1974.