The basic idea behind the name Naga is derived from the idea of a serpent. A serpent lives in underground holes. A person who dwells in underground caves lives like a snake! Such a person is Naga. In other words, an underground cave-dweller is a Naga. Such dwellings are there in India. They are also there in Africa, Europe, Andes and Polynesian islands. The names in these places sounding Naga prove that the concept or idea of Naga came from Indian / Vedic society.
Reading this one may wonder why then Nagaland is called so, as it is mostly mountainous and not an underworld dwelling. Nagaland is situated on an extension of a mountain range called 90 degree East Ridge that is submerged in the Bay of Bengal from south to north direction ramming into India near Bengal. It is made up of hot mantle that has erupted from the ocean bed. Such formations would give rise to underground passages and caves once the hot mantle ran away or cooled.
Read: the symbolism of Tripura samhara by means of Naga as the string of Shiva's bow.
The core of the earth is said to be the foremost snake, the Adhisesha. It is because of the core, the earth remains intact.
It is for this reason Shiva or Naga prathishta is seen in underground holes in many places. Popular examples are Kusheshwar, the original deity of Dwaraka before Krishna moved there. This deity is installed under the ground. Balarama’s last place of departure was in an underground hole in Mukti Dwaraka. Balarama is considered as the avatar of Adisesha. The Shiva linga in Brahma's temple at Pushkar is an underground cave. These are Naga dwellings. The people who lived in such places (underground) were Nagas. The deities having connection to snakes (Shiva and Balarama) were also associated with underground places.
Another type of snake is the life form, our jiva or the soul – which is what we are in our inner self. The soul or jiva gives life to the body and is of the size of our thumb according to Upanishads. It resides as a coil of a snake in the tail of the spinal cord. The very purpose of meditation is to rouse that jiva. It is characterised as a serpent lying dormant within us. Almost everyone would have had a dream of snake some time in their life. It is due to the nature of this snake- like jiva. When aroused through Yoga or meditation or breathing procedures, this snake- like jiva (called Kundalini) rises up.
It is here another entity of Hindu Godhead is connected. After deluge – during cosmic devolution, where would the snakes (jivas) go? They are infinite (ananta) and are held by Vishnu or Narayana in sleeping posture (on the snake bed). When the physical worlds spring up again, these serpents (jivas) enter them and start new life. By this logic every human entity can be called as a Naga! But by the logic of being a cave-dweller in early period of evolution, the identity of Naga has stuck with many people around the world.
Uraga (pronounced as 'Ooragan') is the name of God when appeared in the form of Adisesha, the chief of snakes. There is a temple for Narayana as "Uragan" or "Ooragatthan" in Kancheepuram. The name ooragan signifying the snake (as it crawls) in Tamil must have become Uraga (उरग).
Pannaga is also the name of certain Naga people. According to Puaranas, Nagas were those born to Surasa and Pannagas were born to Kadru. Both Naga and Pannaga mean snake. By this meaning and by the Puranic story of Surasa and Kadru as among 13 wives of Kashyapa, people tend to dismiss these names as figments of imagination. Kashyapa is the progenitor name of mankind. Even now if someone says that one doesn’t know the gotra in which one is born, one can take up Kashyapa gotra. This shows that Kashyapa is the ancient and common ancestor or progenitor of human race signifying the male component (Y chromosome). The 13 wives of Kashyapa indicate the 13 different types of mtDNA of different progenitor female components. If we think in these lines we can understand that Surasa and Kadru are some names of ancient lines of population. It is like Daityas and Danavas coming in the lines of Diti and Danu.