I didn't know what this was either but i found this on the internet about trapped souls. Not sure how accurate it is but i hope it helps:
An experience of psychic loss or entrampent. In certain traditions, harmful practicioners curse you by trapping a portion of your energy body and preventing it from returning to your body. Some consider this portion to be a part of your soul. You do not lose your soul itself, but what is considered a fragment or shard of your soul, in shamanic traditions.
Traumatic expereiences can cause parts of our energy to fragment. If we do not heal and rest to integrate them, the trauma can cause them to leave our proximity and hide in the other worlds for safety. Healing, either of a shamanic, or traditional nature, can usually coax these parts back to us, unless they are purposely blocked by another.