The term Kundalini comes from Kunda, which means a circular object. Usually Kunda is used for artificial water bodies which are circular in shape. They are small ponds. Kundal is a term evolved from Kunda and it simply means circular shaped amulets worn in ears or around wrists. The suffix ‘ini’ is used for feminine things–so Kundal and ini make Kundalini. It generally stands for a feminine natural force which is mysterious and circular in shape and resides at the base of spine in every human being.
The yogic lore is full of hymns addressed to this mysterious force. Russian mystic George Gurdjieff used to say that this tool was put as a buffer in the ancient man and it makes humans fulfil their desires via dreams and imaginations instead of actualizing them in reality–but later on it was removed from the design and still people imagine it to be there. He called it Kundabuffer because it was needed to absorb the shocks which would otherwise damage the human system and wake him up from the deep slumber he always stays in. Gurdjieff was a strange man and his ideas are not easily understood, yet they have some truth.
I will take following two models to tell you about the Kundalini:
Humans were designed by an alien species which is very highly evolved. The tool Kundalini was kept inside them to do two-fold function-one was to keep them in slumber until they were not ripe enough to awaken. This tool, like Gurdjieff said, used to absorb shocks and they lived in forgetfulness and oblivious to all horrors and existential nightmares around them! When time was ripe, the very same tool offered a conduit of energy to higher psychic centers making it impossible to sleep and humans used to become more evolved and awakened.
Kundalini is Maya. The creatrix, the mother, the divine force which created the universe. The illusory potency of the supreme personality of godhead which helps him in creation, sustenance and destruction of all universes. This force is present in form of an energy conduit in all bodies. In humans there is a potential of awakening to realize divine. Maya works as Vidya or Avidya. In form of Avidya, inside humans and other animals, it exercises its power via two modes of ignorance(inertia/tamas) and passion(rajas.) It keeps them oblivious to the impermanence of all pleasures. It makes them dream happiness among all existential nightmares.
When it’s time to wake-up, it acts as Vidya, in form of Sattva(Harmony) and makes them realize all the horrors first. The shocks are not absorbed anymore, they give immense jolts to the nervous system. Detachment and discrimination develop when holy company is found by divine grace and humans start meditation and prayer. Then this Vidya starts transforming their body and mind to divine body and mind. Light starts increasing inside them and darkness fades by and by. A time comes when illumination is total and Kundalini is no more. Only self remains. Only God remains. Only light remains.
image courtesy: oneworldretreats.com