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
American idioms English vocabulary. Английский словарь американских идиом. 2012