You can't really call it music; more like listening to a combination of different tones or frequencies. In fact it is strikingly similar to white noise on a television. It doesn't sound particularly wonderful but the affects it has on the brain is intriguing to say the least.
When these tones are played into each ear simultaneously via stereo headphones, your mind interprets it as a third unique sound. The sudden change in frequencies has a balancing effect on the brain hemispheres, which can be felt as a shift in ones conciousness or a change in mood. The effects depend on the combination of sound frequencies used.
You can get Binaural Beat recordings for a whole host of things. For example, there are tracks to improve concentration, relieve pre exam nerves or to help insomniacs fall into a deep, well needed sleep. You can even get Binaural Beats to put you into a deep meditative state, similarly achieved by the most spiritually advanced of our kind, who have dedicated their lives to the art of meditation.