Flame Imperishable
From Tolkien Gateway
The Flame Imperishable possessed by Eru alone, seems to represent the creating spirit or aspect of Ilúvatar. The power to give life and substance, through it he granted free will and true life to the beings he created. The Ainur and Eä were made through it.
Melkor was envious of it and sought it in the Void but the Flame was only with Eru.[1]
Also called the 'Secret Fire'.