In my experience 'Orthodoxy' has come to mean many things. In my area, when it is said of someone, "Oh, he's from the orthodox church," it usually meant as a slur against his character, that he is narrow-minded, or staunchly conservative, living in the past. It is a way of suggesting that such a person is unwilling to tackle the hard things in modern life, to really deal with the issues that beset the Christian of today. An orthodox person will not recognize, for example, that a true Christian has struggles with his homosexuality, and will not minister to him, but rather just condemn him.
Unchecked, a conversation about someone who is labelled 'orthodox' will go in this direction, on the average.
I have friends and family in that kind of group. It is inconceivable to them that they are doing the very things to the orthodox that they blame the orthodox for. They believe that they are as right as they can be. So they hold the definition of the word for themselves, but the word itself is a negative term to them. But when challenged, the common resort is to hide behind the idea that the Bible is open to each person's interpretation, and that no one really knows what the truth is. If you continue to back them up on their ideas, they only fall back on such an attempt as solid proof that their original idea of narrow-mindedness and oppositional character is right. In other words, they are stubbornly opposed to orthodoxy, not logically.
In our day, I think, it is not enough to define orthodoxy by grounding it in the past. I think that the past is a witness to the lasting power of othodoxy, but we need to be ready to re-prove at every minute what the truth is that is inherent in orthodoxy is. We cannot just be satisfied with upholding the traditions, though we do need to do that. (2 Thess. 2:15 ) We also need to be able to test for the truth. (1 Thess. 5:21 )
I think that the lack of this in our day has led to the existence of many factions in the churches, split over mutually exclusive ideas, but without the resolve to overcome the differences. I have witnessed a few times now that ministers of the Word take it upon themselves, without ecclesiatical consent, to dictate a resolution, when it is clearly in the province of churches and Presbyteries to do that. Even the Apostles did not settle things on their own authority, but held counsel with the elders, before the assembly, on the matters in question. Paul could easily, on his authority, have settled the dispute in Antioch, but he didn't. That is the principle that Jesus instituted when He said that we are not to lord it over each other, that we are not to call any man our father or prior. (Matt. 20:25)
The idea of orthodoxy is very strange to the minds of many in our day, for the concepts of modernity have taken deep hold, even in the church. The text note in the NIV study Bible on John 8: 31, 32 suggests a dichtomous view of truth among Biblical scholars. (I'll see if I can find it, but I don't have it handy by any means. ) The idea of freedom to know the truth, or that truth is sufficiently discernible to settle differences is deemed as arrogance and lack of toleration in our day.
That is not at all what orthodoxy is, of course. People don't like having their hiding places exposed, so they retaliate with ad hom attacks. We need to be firm, yet gentle, in holding to the positions that the churches have always held to, as witnesses for us that we are not standing as some renegade or lone wolf, even if everyone else is of a different persuasion. But we need to be able to derive the truth from the revelations God has given us to discern. And He has revealed Himself by two means, in the creation and governance of the world, and more clearly and fully in His Word.
So to put in very succinct terms, orthdoxy is holding the truth in love.