Essence

The manifestation of one's being

Spirit

There are two key aspects to living beings: Physical Form and Essence
When one dies, their Essence leaves their Physical Form
If something is keeping them from moving on (for instance, a strong desire to remain), their Essence will form into a Spirit of some kind
If they're ready to move on when they die, their Essence disperses and they cease to exist
The Essence still remains in the world, but not in the form of a Ghost

If something completely erases one's Essence, all memories of them fade
Their impact on the world remains, but nobody remembers who they are
People who they were more important to may remember they existed, just not who they were
Others won't have a clue

Abyssal Absorption / [[Condition-2005]] affects both Physical Form and Essence