AUM, also written as OM (Sanskrit word), originated as a mystical trisyllable in the Upanishads and is considered the foundation of all traditional Sanskrit and yogic mantras. The vibration of AUM encompasses all that is, was, and will be, beyond the three forms of time. It is this esoteric vibration that infuses the universe with life and consciousness.
Spiritually purified individuals or those striving to accomplish this can achieve a sense of great harmony, or Shanti (Sanskrit for peace). The mantra consists of three sounds - A, U, and M - with the first two vowels blending to produce an O sound. The A sound originates in the back of the mouth while the M is made with the lips closed at the front of the mouth. When chanted, the sound is prolonged to evoke a meditative state. Sometimes it is translated as meaning the universal sound of all creation. I like chanting it three times in a row with the final OM having a strung out M sound at the end, so you really feel the vibration. The OM is a very powerful symbol that has endured for a very long time and represents spiritual awareness and purification.
It can also be used as a sacred symbol in some forms of energy healing, meditation, and crystal grid work. While others use OM to promote peace through artistic and written forms of it. If you feel called by this symbol try using it in a variety of ways and see what resonates with you most.