'Orthodox' refers to teaching that conforms with already established doctrine. That is, doctrines of the Bible, expressed in the historic creeds and confession of the Christian church. It literally means 'straight teaching.'  (The orthodontist 'straightens' one's teeth.) Orthodoxy (straight or true teaching), is akin to  'orthopraxy,' a term which refers to a right or established practice.  Around the time our denomination was formed (1936), it was originally called the 'Presbyterian Church of America,' but had to be changed because the Presbyterian Church in the USA, the denomination from which we came, said that it was too close to their name. So the founders of the newly established, bible-believing denomination changed the name to 'The Orthodox Presbyterian Church.'