Sakshi or Shiva, along with Shakti (will/energy/motion), represents Brahman, the totality itself in its most fundamental state, the concept of all mighty, revealed in ancient philosophical texts of Hinduism.
It is the Atman, the unchangeable eternal Reality, Pure Consciousness, self-luminous and never itself an object of observation.
It has four parts (akāra, ukāra, makāra and ardhmātra) due to the difference of sthula (gross), sukshama (subtle), bija (causal) and sakshi (witness).
[6] Sakshi means Ishvara, the चेता (cetā), the sole Self-consciousness, who is the witness of all, who gives consciousness to every human being, thereby making each rational and discriminatory.
[7] Vedanta speaks of mind (chitta), or antahkarana ('internal instrument'), and matter as the subtle and gross forms of one and the same reality.