What is a soul in 40k universe? This is a hard word to describe for me.

For a human in 40k they have souls. So when they die, what happen to the soul? If I understand it correctly, when a man dies, his soul goes to the Warp and then what? I mean, is the soul a person with feeling and personality? And what part of the Warp is the man's soul at. Does the soul battle against Chaos power? I know if in life u are a Chaos worshiper, your soul belongs to that chaos power.

Many xeno uses soul for many purpose, but GW never explain what the soul is and what it is for if it does not belong to Chaos power or a meal to C'tan or Dark Eldar.

Does Servertor (sp) have soul? If they are human w/ no feeling (a zombie like) but still alive with soul, can Chaos ever possess them? I can see an army of Servertor sent to fight Chaos in the warp with that idea.

If a human who were good in life and follow the Emperor, when he dies does he live along side the Emperor in the warp? If there are no God(as in our God, Buddha, etc. . .) then there are no heaven... so what happens to soul?

Anyway, What is a soul in 40K?