Om: Symbol of the Absolute

"The goal which all the Vedas declare, which all austerities aim at, and which men desire when they lead the life of continence … is Om. This syllable Om is indeed Brahman. Whosoever knows this syllable obtains all that he desires. This is the best support; this is the highest support. Whosoever knows this support is adored in the world of Brahma."~ Katha Upanishad I

Om or Aum is of paramount importance in Hinduism. This symbol (as seen in the image on the right) is a sacred syllable representing Brahman, the impersonal Absolute of Hinduism — omnipotent, omnipresent, and the source of all manifest existence. Brahman, in itself, is incomprehensible; so a symbol becomes mandatory to help us realize the Unknowable. Om, therefore, represents both the unmanifest (nirguna) and manifest (saguna) aspects of God. That is why it is called pranava, to mean that it pervades life and runs through our prana or breath.

See also:
Om in Daily Life
The Eternal Syllable
The Music of Om
The Vision of Om
The power of Om