ॐ apart from the normal Om sometimes also refers to as omkara (ओंकार oṃkāra) or aumkara (औंकार auṃkāra). Like Ik Onkar ੴ. Sentences/phrases/scriptures can start from Om ‘ॐ नमः शिवाय‘ or even end at it हरिओम
Some of its definitions:
bhūtaü bhavad-bhaviùyad-iti sarvam Omkāra eva
(What had happened before, what is now and what will be later – everything is just Om)
Sometimes referred to as praṇava, literally “that which is sounded out loudly”.
Sometimes it is defined as “the sound of the universe”
Michael Carroll, dean of the Kripalu School of Yoga. said “It’s big. Om is nebulous, and it’s vague. It can mean almost anything.”
ॐ signifies slew of trios:
The heavens, earth, and the underworld
The Hindu gods Brahma, Vishnu, and Shiva (aka creator god, sustainer god, and destroyer god)
The waking, dreaming, and dreamless states are some of it
The A (aahhh) sound represents the creation aspect of the universe and all of the gross objects within it. Ahh is the beginning of all sounds. With this syllable you experience the existence of the world through the activity of the senses.
The U (oooh) sound signifies the maintaining energy of the universe and the subtle impressions of the mind. It connects us to an inner sense of something greater than that which we can see and feel with our senses.
The M (mmmm) sound characterizes the transformative energy of the universe and the thoughts and beliefs of your beingness. This sound unites you to the awareness of oneness.
The fourth sound is silence or anagata. It is the vibration which is beyond verbal pronunciation. It is pure consciousness of the Self or the Atman
One of the hypothesis/belief further goes that when we sound om together, we’re aligning body/mind/spirit; we’re aligning with one another; we’re aligning with the universe because it’s the sound of the universe and we’re referencing sometcurve.
1 –This curve represents the waking state.
2 – This curve represents deep sleep or the unconscious.
3 – This curve represents the dream state (which lies between waking and deep sleep)
4- The dot represents the absolute state of consciousness which illuminates
all other states of consciousness.
5 –The semicircle represents माया (or the veil of illusion.) it separates
the absolute from the other three curves.
Source: Meaning of ॐ….