Truename is basically the soulname
or the proper essence
of a being. It often results in the invention of new words, but it necessary to describe a being or even a thing, truly and properly.
one such example... in reference to a dog i know, a dog that *looks* vaguely wolfish, and also looks vaguely like a wolfhound (one of the few remaining unspoiled, free breeds). this dog looks wild, looks like it has wolf-spirit, freedom, *life*. you *meet* this dog and it is as simpering, fawning, 'yes-master-what-can-i-do-for-you-now-master-you-are-wonderful-'ing a dog as i have *ever* met.
to describe the nature of this dog, this dog's essence, i do not refer to the dog by her name. nor do i call her 'the flat-coated retriever' (which she is) because these things do not *describe* her they do not capture her *essence*. whenever i refer to this dog i call her the 'hollow-wolf'... and anyone who understands the concept of essence or soulname *immediately* understands which dog i am talking about, even out of a large group of dogs.
when a truename is discovered, it becomes immediately apparent to the discoverer that there could not *be* another possible soulname for this person or creature or thing. it is *known* *felt* *sensed*, not intellectualized. when the word, the name, the phrase is so full of meaning and rightness in the context that it feels like it is going to *explode*just from the sheer energy and power and beauty contained in its truth, *this* is soulname *this* is truename...
soulname or truename (there called "true name" as two words) is additionally explained beautifully in a an otherwise completely mediocre book called "Wizard's Hall" by Jane Yolen. Its quite fascinating, if by far weaker than most of her other books...