avadhūti (Sanskrit). The central channel (nāḍī) or pathway of psychic energy that runs through the human body, according to the spiritual physiology of anuttara-yoga-tantra. This channel is visualized as a fine tube, pale blue outside and oily red inside, running up along the spine from the perineum to the point between the eyebrows with four or five cakras or energy centres situated along it. It is normally sealed at the ends and at the junctures with the cakras but can be opened to allow the entry and free flow of the subtle energy of ‘wind’ (vāyu) from the two adjacent channels, the lalanā and the rasanā, to actualize the knowledge (jñāna) of the dharma-kāya or ultimate reality.

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)