A flat paper container with a sealable flap, used to enclose a letter or document.
Envelope
a written, typed, or printed communication, especially one sent in an envelope by mail or messenger.
Letter
a card, often with a photograph or picture on one side, that can be sent without an envelope
Postcard
a metal container in the street or other public place in which you can put letters to be mailed
postbox
a place where you can mail letters or packages and buy stamps, or infml the US Postal Service
Post office
