Ânandamaya-Kosha (Sk.). “The illusive Sheath of Bliss”, i.e., the mâyâvic or illusory form, the appearance of that which is formless. “Bliss”, or the higher soul. The Vedantic name for one of the five Koshas or “principles” in man; identical with our Âtmâ-Buddhi or the Spiritual Soul.
Source: H.P.Blavatsky - The Theosophical Glossary