noun
fourth-class mail
A category of domestic mail in Japan for certain printed materials, educational materials, and other specified items, offering lower postage rates.
第四種郵便物は、通信教育の教材などに利用される。
Fourth-class mail is used for correspondence course materials and the like.
Compound of 第四 (fourth), 種 (kind/class), and 郵便物 (mail item). The term reflects the Japanese postal classification system.