Orthodox is a word about beliefs. It is made from two Ancient Greek words, ὀρθός orthós „correct, straight“ and δόξα dóxa „teaching, worship". Orthodoxy means a teaching that is supposed to be close to the original.

In particular:

in Christianity:

• Eastern Orthodox Church (The split of the Christian Church into the Roman Catholic Church and the Eastern Orthodox happened in 1054, in what is known as the Great Schism)
• Oriental Orthodox Church (Split from the rest in the 5th century, at the Council of Chalcedon)
• Theologically traditional often in all lower case-- orthodox

in Judaism:

• Orthodox Judaism
• Modern Orthodox Judaism

Jewish organisations:

• Orthodox Union