Orthodox is one who faithfully follows a principle, a norm or a doctrine. From the Greek “orthos” meaning “upright” and “doxa” meaning “faith”. It is what is in accordance with the religious doctrine taken as true.
Orthodox is an expression used to refer to something rigid, traditional, that does not evolve, that is conservative, that does not adapt or admit new principles or new ideas. It is one that conforms to the traditional principles of any doctrine.
The expression, “unorthodox” is used to refer to that individual or something that does not follow any traditional rules, that deviates from what is common, from what is conventional.
Orthodox is one who belongs to or is a follower of the Orthodox Apostolic Catholic Church, also called the Orthodox Church and the Church of the East, which resulted from the refusal of priests and bishops of the East who did not accept the modification imposed on the Creed, at the Council of Toledo, because they believed that the Holy Trinity is one and indivisible. The split actually took place in 1054, made official by Pope Leo IX. Christianity was divided into two churches: Western Catholic and Eastern Orthodox.
Orthodox and heterodox
While orthodox means rigidity, fidelity, the expression heterodox, refers to one who is not orthodox, who is contrary to the principles, beliefs, and dogmas of a religion.
Heterodox is an adjective that means heretic, that is, it refers to heresy, a doctrine that is contrary to what is defined by the church in matters of faith.