Aamod

Linga (Mark, Symbol)- Samkhya tradition refers linga as "that which hascharacteristics" namely the human personality which includes Antahkarana(its aspects - ego, subconscious, conscious thought and intellect,5 cognitive senses (jnanedriyas), and 5 conative senses (karmendriyas).

Maitraayaniya Upanishad (VI.10) applies the term linga to 'the entirecreation extending from the first principle (Mahat) to the particulars(vishesha)' and contrasts it with linga 'without origin' i.e God itself.

Mahabharat (XII.195.15) describes linga as the vehicle, or body of thetransmigrating psyche (that which passes from one birth to the next).

Metaphysically, linga stands for the unimaginable potency PRIOR to thecreation of universe.
Abhinav Gupta in his Tantra- Aaloka (V.54) explains Linga as "linam-gamyate - This whole (universe) is dissolved (linam) in that, and thiswhole (universe) is perceived (gamyate) as residing within that".

The 'Amaraugh- Prabodh' offers following etymological definition: "Wherethe movable and immovable dissolves by force of 'Laya' (naturaldestruction), that is (known as) linga.

As the mystic law 'As above so below" -Brahmanda manifests in every Pinda, the cosmic linga has its representation within human body also.

ThusTantric and Hatha Yoga literature describe experience of radiant linga indifferent psychic centers (chakras) of the body.

Brahma Upanishad speaksof 3 types of linga that should be made object of meditation: Adho lingaat the base of spine (Mulaadhaar chakra), Shikhin linga at the crown ofthe head (Sahasraar chakra) and Jyotir (light) linga at the center of theforehead (Aajnyaa or Guru chakra).
Siddha Siddhanta Paddhati (II.4) mentions a linga shaped flame in theheart.

The stone in its spherical form untouched by the sculptor, is the form nearest to the formless. And the sexual union of male and female is the farthest the human mind can reach to express the creative action of God. This action, as God Himself, remains a mystery to man. All that man can do is to look at nature and see how a new being comes into existence. Since nature is the work of God, it is logical to conclude that both the male and the female principles must be found in God Himself, the sexes being only a manifestation of God’s nature. At the level of symbolism, the Shiva Linga or the stone with the semi-spherical top, makes a positive contribution in man’s effort to express the Divine Mystery.