Parama Siva is the Parameswara (supreme God) in Sanatana Dharma. This term refers to the highest Tattva that is above everything else. Him which nothing (anything, anyone) can surpass is Parameshwara. He is the Ishwara (God) of the world, time, all living beings and inanimate objects – Isha, Lord, protector. He can be described as Sarveshwara, Akhileshwara, Nikhileshwara. Which means he is almighty God, the absolute God.
Because He is the God of the world, He is called Vishweshwara, Vishwanatha, and Jagadeeshwara; because He is the lord of time, He is Mahakaal and Kaleshwara; because He is the protector of all beings, He is Pashupati, Jeeveshwara; and because He is god of Bhootas (the elements) He is Bhooteshwara. Because He is the god of Sookshma Lokavaasis (astral beings), He is Sureshwara, Devadeva (God of the Gods), and Mahadeva. Because He is the God of Karana Lokavaasis who are symbols of Ishwara, He is Maheshwara. “Tameeshwaranaam Paramam Maheshwaram” – because He is god of the gods, He is called Maheshwara. (Swethasvataropanishad 6:7). And because He is eternal, He is Sanathan. Siva: Kevalam Shashwatham Sivamachyutham (Taitteeriya Aaranyakam 13-7) Siva Tattva is that absolute reality which is eternal and unchanging.
Eka Parabrahma Tatva
It is this single Parabrahma Tatva that the Aarsha Guru Paramparas revered as Parameshwara, Mahadev, Maheshwar, Pashupati, Mahakaal, Sanathan, Ajaikapath, Ahirbudhnya. Paramasiva is the Tatva Nama of Parameshwara.
“Na tasya kaschith pathirasthi loke” – there is no refuge, protector, or God above Parama Siva (Shwethashvataropanishad 6:9). The names Sivam, Parama Sivam, Siva, Parama Siva are all Tattva Namas that refer to the Nireeswara (one who has no God above him), Nirashraya (one who needs no refuge), Sanathana (eternal), Parameswara which is the single Parabrahma Tatva. He is Nitya – Suddha – Buddha – Mukta. He is Akaaya (one who does not have physical, astral, or causal bodies), Nirakara (without form), and Niravayava (without organs).
Sivalinga is a symbol of this formless Parabrahma Tatva. The early Yogis meditated upon the Jyotirlinga that appears in the Dhyana – Samadhi of Yogis. That is the Jyoti Dhyana Vidya Rahasya. Look at the meaning of the Gayatri Mantra – the essence of the Mantra is that may Parama Siva’s Jyothi that enlightens the physical-astral-causal worlds enlighten my wisdom. Later the stars that illuminate the physical world, sun, moon, Agni, lamp, etc., were used for meditating. (Some Tantriks and Yogis still meditate on Agni during Shivalingopasana). Later, meditating upon symbols made of metal or stone representing the Jyotilinga became commonplace. One can find a variety of shapes of Sivalingas amongst the Dwadasha (12) Sivalingas itself. These are to aid devotees who are at different levels in Upasana.