A God or Goddess is a magical being who is only able to influence the world by mortal beings. When they want to show themselves, they change magic into light and shape it into a being.
|Spoilers from "Voice of the Gods"|
Gods cannot enter voids, to do so would kill them as they are magic. One can become a god after becoming immortal. To kill a God, you trap them inside a pocket of magic within a void and empty the magic around them.