Is orthodox Catholic or Protestant?

The Orthodox Church is one of the three main Christian groups (the others being Roman Catholic and Protestant). Since the Eastern capital of the Roman Empire was Byzantium, this style of Christianity is sometimes called Byzantine Christianity.

What makes Orthodox Christianity different?

Orthodox and Protestants reject Papal infallibility and Papal supremacy. Orthodox Christians are not under the authority of the Pope. They are under the authority of various Patriarchs. Encouraged in the Catholic & Orthodox Churches; most Protestants only pray directly to God.