mail - order -bride · mail - order -brides · mail - order house · mail-ordered; mail - ordering. mail-orders · mail program · mail protocol · mail proxy · mail reader. Definition of mail order company: Companies which list their products for sale in catalogs or websites for consumers to buy via telephone, mailed check with. advertising that creates orders for purchase through the mail. Mail - order advertising can utilize almost any form of media, although catalogs, such as the Spiegel.