When a being is brought in existence it's footprint in the Ocean of Fate is what some call a Soul. Each soul has it's own level of power. This can change during that creature's life, some grow some shrink - some have special properties, depending on whom it belonged to.
The other property all Souls have is that they each possess a unique signature. A feeling, although depending on who's the recipient it can take a variety of forms. Most supernaturals such as sorcerers, faes, demons etc call these True Names.
Knowing one's True Name gives you extreme power as it allows those with the knowledge to find the Soul even in the darkest depths of the Ocean of Fate and manipulate it, or even destroy it.