From Hindupedia, the Hindu Encyclopedia
By Swami Harshananda
Ānandamayakośa literally means ‘the bliss sheath’.
One of the five sheaths, the pañcakośas, it gets its name due to the experience of joy in suṣupti or deep sleep. In content, it is identical with ajñāna or nescience. Since it makes the jīva, the individual soul, forget his nature as pure ‘caitanya’ or consciousness, by covering it as it were, like a kośa or sheath, it is termed as a ‘kośa.’ It clings to the soul till the state of liberation.
- The Concise Encyclopedia of Hinduism, Swami Harshananda, Ram Krishna Math, Bangalore