The Auric Twin phenomena is usually referring to a type of spirit body attachment that is acting as a parasitic twin to the being, and may need to be removed or cleared to remove energy parasitism.
This can be the result of mismatched body parts, that can be an organic or inorganic event. Sometimes this a result of Soul Fragmentation, Negative Form, Artifacts or from types of alien or dark manipulation like Black Magic. For whatever the reasons, it is generally beneficial to clear this attachment from draining energy from the etheric body double of the person.
Term first found: Page 84, HGS Manual