The Meaning of Om

Aum (also Om, ॐ) is the most sacred syllable in Hinduism, symbolizing the infinite Brahman and the entire Universe. The syllable is sometimes referred to as the "Udgitha" or "pranava mantra" (primordial mantra); not only because it is considered to be the primal sound, but also because most mantras begin with it. It first came to light in the Vedic Tradition. As a seed syllable (bija), it is also considered holy in Esoteric Buddhism.

The symbol of Om contains of three curves, one semicircle and a dot. The large lower curve symbolizes the waking state; the upper curve denotes deep sleep (or the unconscious) state, and the lower curve (which lies between deep sleep and the waking state) signifies the dream state. These three states of an individual’s consciousness, and therefore the entire physical phenomenon, are represented by the three curves. The dot signifies the Absolute (fourth or Turiya state of consciousness), which illuminates the other three states. The semicircle symbolizes maya and separates the dot from the other three curves. The semicircle is open on the top, which means that the absolute is infinite and is not affected by maya. Maya only affects the manifested phenomenon. In this way the form of Om symbolizes the infinite Brahman and the entire Universe.

Origin
Found first in the Vedic scriptures of Hinduism, Aum has been seen as the first manifestation of the unmanifest Brahman (the single Divine Ground of Hinduism) that resulted in the phenomenal universe. Essentially, all the cosmos stems from the vibration of the sound 'Aum' in Hindu cosmology.

Philosophy of AUM
According to Hindu philosophy this syllable is combined of three components: the letter A (alpha), which represents creation, when all existence issued forth from Brahma's golden necleus; the letter U, which refers to Vishnu the god of the middle who preserves this world by balancing Brahma on a lotus above himself. The letter U with the A, produces the sound of the long O (omega). The M produces the prolonged resonance of the nasal cavity with the mouth closed: it is the final part of the cycle of existence, when Vishnu falls asleep and Brahma has to breathe in so that all existing things have to disintegrate and are reduces to their essence to him. This is the M of Mahesha, also known as the great Lord Shiva, whose long period of yoga begins so that the sensual world ceases to exists.

When you pronounce AUM:
"A - emerges from the throat, originating in the region of the navel U - rolls over the tongue M - ends on the lips A - waking, U - dreaming, M - sleeping It is the sum and substance of all the words that can emanate from the human throat. It is the primordial fundamental sound symbolic of the Universal Absolute."
In fact, when correctly pronounced, or rather, rendered, the "A" can be felt as a vibration that manifests itself near the navel or abdomen; the "U" can be felt vibrating the chest, and the "M" vibrates the cranium or the head. The abdominal vibration symbolises Creation; It is interesting that the "creative" or reproductive organs are also located in the lower abdomen. The vibration of the chest represents Preservation, which is also where the lungs are situated (the lungs sustain or preserve the body through breath). The vibration of the head is associated with Destruction or sacrifice, since all that gives up or destroys is first destroyed mentally. Hence, the entire cycle of the universe and all it contains is said to be symbolised in AUM.

Por favor leiam o texto completo em http://en.wikipedia.org/wiki/Aum#Aum_in_Hindu_tradition, onde estão descritas explicações do Om segundo outras filosofias que não a Hindu.

Namaste!!