First, AUM is not a word, it is a pure sound, so it has no meaning as such. It is a pure sound, like the sound of a waterfall; what meaning has it? - no meaning at all. Or the sound of this aeroplane passing by; what meaning has it? - no meaning at all. The sound becomes a word when meaning becomes attached to it. A meaningful sound is a word; a meaningless word is a sound. So the first thing to be understood: AUM is not a word, it is pure sound. All other words have arisen out of it, but it itself is not a word. It is the source of all sounds; it cannot have any meaning whatsoever.

This sound AUM consists of three sounds: A, U, M. These are the seed sounds; all other sounds are created by A,U,M. All our words, the whole alphabet, is created by these three seed sounds:

A,U,M. AUM is the source of all these three.

That's why in India AUM is not written alphabetically. It has a symbol of its own. That is simply to designate: don't be confused and don't try to think about AUM as a word. AUM is the only sound in India which is not written alphabetically. It is written pictorially; it has a picture, a symbol, which is outside the alphabet. These are symbolic things. It has been kept outside the alphabet because it is the source. The source is always out, beyond, transcendental.

AUM consists of three sounds and one anuswar. Anuswar is a very subtle sound; it represents a kind of humming. When you say, "AU", that M prolonged, that humming sound that goes on reverberating, is the anuswar. Anuswar means just a dot; that too represents something. So AUM consists of four things: three visible, A,U,M, and the fourth invisible the rhythmic, humming shadow.