Tummo is a practice associated with the subtle body of energy-channels, energy-winds and energy-drops. The practices are taught in a suite of advanced sadhana, such as the Six yogas of Naropa, which are contemplative practices, spiritual energetic work or meditations in the Himalayan traditions of Vajrayana and Bön. This discipline is key to a suite of advanced sadhana or spiritual disciplines in Tibetan Buddhism. Himalayan disciplines like Yantra Yoga work with this "inner heat": where yantra is the synonym for asana .
In common currency Tummo is related to the description of intense sensations of body heat, that are held to be a partial effect of the practice of Tummo-meditation. Tummo is taught as one part of the six yogas of Naropa. Stories and eyewitness accounts abound of yogi practitioners being able to generate sufficient heat to dry wet sheets draped around their naked bodies while sitting outside in the freezing cold, not just once, but multiple times. These observations have also been discussed in medical articles (Ding-E Young and Taylor, 1998).
http://en.wikipedia.org/wiki/Tummo
http://en.wikipedia.org/wiki/Six_yogas_of_Naropa
The meditation for producing psychic heat provides a factual basis for the somewhat melodramatic stories of Tibetan monks who, on an icy cold night, dry out a series of wet sheets wrapped around their unclad bodies. It can be done, by any ordinary human being--with proper instruction and practice--and so, as with other physical exploits such as "fire-walking," represents nothing particularly magical or mysterious. The secrets here are matters of mastering specific meditation techniques, and applying them with a focussed mindfulness. This is not at all to disparage such accomplishments, for among practicing lamas and members of the spiritual community, or sangha, the psychic heat meditation, or gTummo, is believed to establish the essential foundation for opening oneself up and becoming able to absorb the higher teachings of all six Yogas of Naropa.
http://www.csus.edu/indiv/v/vonmeierk/2-04SIXY.html
