Om

Om
"Ahh-Ooo-Mmm"  |  "AUM"
A universal sound like "Amen."  It is the sound of Creation, the divine all-encompassing consciousness in the form of an original vibration manifesting the divine in our bodies.  It is the reflection of our absolute reality, our existing without beginning or end, and embracing all of existence.  The mantra Om is the name of God, a vibration of the Supreme.
Letter by letter, A-U-M conveys the divine energy (Shakti) united in its 3 basic aspects: Creation (Bhrahma Shakti), Preservation (Vishnu Shakti), and Liberation and/or Destruction (Shiva Shakti).
It is profound religious meditation, the highest spiritual sound.  A- kara means form or shape like earth, trees, or any other object.  U- kara means formless or shapeless like water, air, or fire.  Ma- kara means neither shape nor shapeless like dark energy that exists in the Universe.  A-U-M.
Om opens the chakras, our third eye.  Om is universal.  It is a safe chant for meditation.
image source  |  Om Wikipedia