It is a term in Eastern spiritualism and yoga, refering to an apparent reservoir of psychic energy at the base of the spine, a chakra in three and one-half turns. Statements such as "It has unlimited energy stored in it and [the] velocity of its energy is... higher than the velocity of light" abound. It is sometimes believed to be an aspect of Shakti?, the goddess and consort of Shiva.
It is a popular concept and is widely quoted among various disciplines of yoga and New Age beliefs.
See also Qi