True Name

From the White Wolf Wiki, the most complete White Wolf reference

A True Name is the name of a fallen that reflects their true nature and identity as a formerly divine being; they were originally granted to them by God to reflect their position in Heaven, and were altered when the fallen were spurned. They are unpronouncable by mortal tongues; rather, they are a collection of abstract sounds and concepts, such as the sound of a hundred children laughing at once or the wind whistling over the entrance of a cavern.

True Names are kept as strict secrets to all but a fallen's most trusted companions, as they can be used against them in many ways. Knowing a fallen's True Name makes it easier to summon them, follow them, or target them as part of a ritual; those who use a fallen's True Name against them also gain advantages against the fallen in mental or social situations. A fallen or mortal with patience can crack a fallen's True Name by examining their identity and purpose, but the name must be known in its entiretly; a fragment of a True Name is utterly useless.

• DTF: Demon: The Fallen Rulebook, p. 255-256