On Usage of the Term ‘Orthodox’

The term ‘Orthodox’ originally came into popular usage in the Eastern Christian world as a descriptor of the church communities in the sixth century, to distinguish those who accepted the decrees of the Council of Chalcedon (451) from those who refused them. It grew up as a party term, therefore, meant to distinguish the Byzantine Christians (and the Latins along with them) from those dissenting from the Christological settlement of Chalcedon. (Fr. John Mcguckin: The Orthodox Church pg. 24)