Orthodoxy is adherence to correct or accepted creeds, especially in religion.
Adherence to the Nicene Creed is a common test of orthodoxy in Christianity.
A creed, also known as a confession of faith, a symbol, or a statement of faith, is a statement of the shared beliefs of a community in a form which is structured by subjects which summarize its core tenets.
Icon depicting Emperor Constantine (center) and the Fathers of the First Council of Nicaea (325) as holding the Niceno-Constantinopolitan Creed of 381