19 CFR 145.1 : Customs Duties (§ 0.1 To Parts 400-599) — (§ 141.0 To Parts 193-199) — U.S. Customs And Border Protection, Department Of Homeland Security; Department Of The Treasury (Continued) (§ 141.0 To Parts 193-199) — Mail Importations (§ 145.0 To Appendix To Part 145) — General Provisions (§ 145.1 To § 145.5) — Definitions.

(a) Mail article. “Mail article” means any posted parcel, packet, package, envelope, letter, aerogramme, box, card, or similar article or container, or any contents thereof, which is transmitted in mail subject to customs examination.

(b) Letter class mail. “Letter class mail” means any mail article, including packages, post cards, and aerogrammes, mailed at the letter rate or equivalent class or category of postage.

(c) Sealed letter class mail. “Sealed letter class mail” means letter class mail sealed against postal inspection by the sender.