{n.} A class of mail that is not sealed and weighs a pound or more, that includes things that are bought and sold and sent in the mail, and printed things that are not second or third class mail. * /Bill sent away 98 cereal box tops and a dollar and got back a sheriff's badge and gun in the mail by fourth class./
FOURTH CLASS
Meaning of FOURTH CLASS in English
Dictionary of English idioms . Словарь английских идиом. 2012