Om Namah Shivaya

Om Namaḥ Śivāya is the most holy name of God Śiva, recorded at the very center of the Vedas and elaborated in the Śaiva Agamas.
Na is the Lord’s concealing grace, Ma is the world, Śi stands for Śiva, Va is His revealing grace, Ya is the soul. The five elements, too, are embodied in this ancient formula for invocation. Na is earth, Ma is water, Śi is fire, Vā is air, and Ya is ether, or Ākāśa. Many are its meanings.
Namaḥ Śivaya has such power, the mere intonation of these syllables reaps its own reward in salvaging the soul from bondage of the treacherous instinctive mind and the steel bands of a perfected externalized intellect. Namaḥ Śivāya quells the instinct, cuts through the steel bands and turns this intellect within and on itself, to face itself and see its ignorance. Sages declare that mantra is life, that mantra is action, that mantra is love and that the repetition of mantra, japa, bursts forth wisdom from within.
The holy Natchintanai proclaims, “Namaḥ Śivāya is in truth both Āgama and Veda. Namah Śivāya represents all mantras and tantras. Namaḥ Śivaya is our souls, our bodies and possessions. Namaḥ Śivāya has become our sure protection.”
—Satguru Sivaya Subramuniyaswami

The book “The Ancient Power of Sanskrit Mantra and Ceremony: Volume I” by Thomas Ashley-Farrand defines Om Namah Shivaya as:
“This mantra has no direct translation. The sounds relate directly to the principles which govern each of the first five chakras on the spine…Earth, water, fire, air, ether. Notice that this does not refer to the chakras themselves which have a different set of seed sounds, but rather, the principles which govern those chakras in their place. A very rough, non-literal translation could be something like, ‘Om and salutations to that which I am capable of becoming.’ This mantra will start one out on the path of subtle development of spiritual attainments. It is the beginning on the path of Siddha Yoga, or the Yoga of Perfection of the Divine Vehicle.”

OM/AUM: The three parts of Om (A-U-M) encompass the three states of waking, dreaming, deep sleep, the three levels of gross, subtle, causal, and the three levels of conscious, unconscious, subconscious, as well as the three universal processes of coming, being, and going. Absolute silence beyond the three levels is the silence after AUM. It also refers to Tripura, the one who live in the “three cities” as in Mahamrityunjaya Mantra, as well as the light referred to in Gayatri Mantra.

Namah/Namaha: Adoration, homage, respect. Nothing is mine (as an individual person); everything is thine (as the Absolute Reality). The three levels of Om, the three worlds of gross, subtle, and causal, along with the three states of waking, dreaming, and deep sleep states of consciousness, as well as the three levels of conscious, unconscious, and subconscious themselves are “not mine” as the true properties of who I really am. Truly, “nothing is mine.” Rather, everything, all of these triads is “thine” or the “other” as the Absolute Reality.

Shivaya/Shiva: That Absolute Reality that is the ground out of which the others emerge. It is that “ink,” so to speak, that is not separate from the many forms which may appear to manifest or be created from that ink. In the Realization of this, one comes to see that he or she is one and the same with the Absolute Reality. The Mahavakyas, the great utterances, are seen to be true. Shiva (the static or ground) and Shakti (the active or creative) are seen to be one and the same. She (Shakti), while one with Shiva is realized in direct experience as the one in the three worlds (Tripura) outlined in Om.