/ˈsɜːrtɪfaɪd meɪl/ – Phrase
Definition: Phương tiện gửi thư chứng nhận.
A more thorough explanation: (US) a post office service in which the person sending a letter or parcel receives written proof that it has been posted and the person must sign an official document stating that it has been received
Example: The documents were sent by certified mail.