It is a term in yoga, referring to an apparent reservoir of psychic energy at the base of the spine. Kundalini is curled up in the back part of the root 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.
The force of kundalini is supposed to be raised through meditative exercises. As it raises from the root-chakra up it activates each chakra it goes through. The higher it gets, the more spiritual a person is supposed to be. In raising kundalini spiritual powers (siddhis) arise. These supposedly include clairvoyance of various sorts.