It is the translation of the Greek word Orthodox.
And, that is why in Russian it is called Pravoslavny - correct worship/glorification. In Japanese Seikyo - exactly the same meaning of Correct Worship.
We believe absolutely that ours is the True Faith passed down to us unaltered from the Apostles, as it says in the Creed: "And (I believe) in One Holy Apostolic and Catholic Church." - that is, the Orthodox Church (catholic here meaning universal and for all peoples).