The Ember

-The consolidated energies of all Asterii souls, shaped into a projectile weapon to be launched by the Worldminds in an ultimate attack against a Chaos God. 

 -The Ember was unable to kill Nurgle, but apparently remains a toehold of sorts within the realm/being the Archenemy. It is possible that Lazarus encountered this ember in a dream, surrounded and slowly being encroached upon by gargantuan, organic structures shaped similarly to blades of grass. He was able to rejuvenate the Ember's flickering light using his Redressor . In the process, he learned how to use the device's purge protocol more efficiently. 

 - King Quinque's plan involves creating a larger Ember from the souls spread across the many Worldminds, and launching properly fatal attack against Nurgle. 

 -Remnants of the psychic attack seem to remain in the Immaterium, as small glowing embers; these residues have some role in containing the entity that powers the Worldmind of Asterion.