It does not have one central seat, because each jurisdiction has its own spiritual head, but Constantinople is the seat of the Ecumenical Patriarch, who is considered to be the 'First among equals' in the Orthodox Church.
Eastern Orthodox is a branch of Christianity.
Eastern Orthodox Christianity, Christianity, and Catholic.
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Eastern Orthodox
Both the Eastern Orthodox and the Western Catholic branches of Christianity claim to have the same 'pillars' of religious foundations.
Russian Orthodox,or Orthodox Christianity,both mean the same thing :)
Orthodox Christianity.
Victoria Azarenka's religion is Orthodox Christianity.
Eastern Orthodox Church
Christianity, mostly the Eastern Orthodox Church.
Greek Orthodox
Russian Orthodox, is referring to the Eastern Orthodox Church of Christianity or Judaism, were in Russia, the main religion is Russian Orthodox.