What is Om?

I found this on a yoga website and thought I'd share it with you because it actually explains the symbol's parts...

What is Om?

The sound of Om represents everything. The material world of the waking state is symbolized by the large lower curve. The deep sleep state is represented by the upper left curve. The dream state, lying between the waking state below and the deep sleep state above, emanates from the confluence of the two.

The point and semicircle are separate from the rest and rule the whole. The point represents the turiya state of absolute consciousness. The open semicircle is symbolic of the infinite and the fact that the meaning of the point can not be grasped if one limits oneself to finite thinking.

The semi-circle reminded me of the star and cresent of Islam, but apparently there is no connection.