Koshas can be thought of as sheaths or layers that cover our true self (atman). There are five koshas described in the Taittiriya Upanishad. They are as follows (ordered from the gross to the subtle):
(1) Annamaya kosha
This kosha is the gross physical sheath, that needs food to sustain itself such as skin, bones, flesh, fat and filth.
(2) Pranamaya kosha
This is the vital layer composed of prana (subtle life force) that holds the body and mind together to support a functioning organism. Breath could be considered as a physical manifestation of prana.
(3) Manomaya kosha
This kosha is the mind (manas) sheath which along with the five sensory organs (eyes, nose, tongue, ears and skin) forms what could be be said to be individual identity or personhood.
(4) Vijnanamaya kosha
Vijananamaya kosha is the knowledge or intellect sheath. Vijanana means intellect. The intellect helps us discriminate, but it still identifies with the mind, body and the senses.
(5) Anandamaya kosha
Ananda means bliss and this kosha is said to be the reflection of the self (atman) or the absolute. It fully manifests itself in deep sleep, when the mind, senses and the intellect are not functioning.