"Russian Orthodox," and "Greek Orthodox" Are Strictly Informal Distinctions In The Same Faith

https://ignisdivine.substack.com/p/russian-orthodox-and-greek-orthodox 

 “Orthodox Churches, Eastern: Greek Orthodox Church and Its Theology. The expression “Greek Orthodox Church” has two meanings. In the broad sense, it refers to the entire body of Orthodox (Chalcedonian) Christianity, sometimes also called “Eastern Orthodox,” “Greek Catholic,” or generally “the Greek Church,” because the mother communities of Orthodoxy were all located in the Greek speaking portion of the ancient Roman Empire.