In Moria, when Gandalf confronts the Balrog on the bridge of Khazad-dûm, Gandalf says the following:
I am a servant of the Secret Fire, wielder of the flame of Anor. You cannot pass! The dark fire will not avail you, flame of Udûn. Go back to the Shadow! You cannot pass!
I cannot find any reference to “flame of Anor” or “flame of Udûn” anywhere else in the Lord of the Rings, not in the appendices. As Gandalf possesses Narya (the ring of fire) at this point in time, I am wondering if he is referring to this in some way? Is this correct? If not, what is he referring to?