According to the Vedānta philosophy, the true nature of the human being—for that matter, any living being or even the whole creation—is ātman, the Self. Though this ātman is ever present in us, we do not feel its presence. On the other hand, we identify ourselves with the body and mind, and hence, suffer. The factors responsible for this hiding or covering of our true nature are five: the physical body which is a product of anna or food, prāṇa or the vital energies responsible for the functioning of the sense-organs as also other biochemical processes within the body, manas or the mind, vijñāna or the intellect, also called buddhi, and ajñāna or basic ignorance. These five are respectively called annamaya-kośa, prāṇamaya-kośa, manomaya-kośa, vijñānamaya-kośa and ānandamaya-kośa. Kośa means a sheath. Since these factors cover the ātman like a sheath and are five in number, they are called pañcakośas.
Annamaya-kośa the first, consists of the physical body given by the parents and nourished by anna or food. The five prāṇas or vital energies like prāṇa, apāna and others form the second, the prāṇamayakośa. Manas or the mind with its capacity for cognition, will and doubts comprises the third, the manomaya-kośa. Vijñāna or the intellect, with its capacity to weigh the pros and cons, and come to definite conclusions is the fourth, the vijñānamayakośa. Ānandamayakośa the fifth, is the name given to ajñāna or ignorance. The ānanda or happiness that is enjoyed during deep-sleep is due to it. Hence the name.
Annamayakośa is the outermost cover. Prāṇamayakośa is within it, filling it fully and of the same form. So also manomaya, vijñānamaya and ānandamaya kośas which succeed prānamayakośa in that order, fill their preceding kośas.
By a process of negation, negating each of these kośas as not-self, one can arrive at the true Self.