Chhâyâ (Sk.) “Shade” or “ Shadow”. The name of a creature produced by Sanjnâ, the wife of Surya, from herself (astral body). Unable to endure the ardour of her husband, Sanjnâ left Chhâyâ in her place as a wife, going herself away to perform austerities. Chhâyâ is the astral image of a person in esoteric philosophy.
Source: H.P.Blavatsky - The Theosophical Glossary