Shiva Linga is the holy symbol of Lord Shiva that is considered sacred by the devotees of Lord Shiva. The word, ‘Lingum’ in Sanskrit means, ‘symbol’. Shiva Lingum, therefore means symbol of Lord Shiva and is therefore considered most sacred by Shaivaites. Siva Linga has been worshipped in Hinduism since ages. Worship of Shiva Linga is regarded sacred and superior Shiva Mahapurana. This is because the form makes worship simple while maintaining the truth that God does not have any definite form.

Structure of Shiva Linga
Most prevalent icon of Shiva and virtually found in all Shiva temples, Shiva Linga is a rounded, elliptical, an-iconic image that is usually set on a circular base or peetham. According to some scholars the Peetham represents Parashakti, the manifesting power of God.

Shiva Lingas are usually made of stone that may either be carved or naturally existing - svayambhu, such as shaped by a swift-flowing river. Shiva Lingas may also be made of metal, precious gems, crystal, wood, earth or transitory materials such as ice. Some scholars say that transitory Shiva Linga may be made of 12 different materials such as sand, rice, cooked food, river clay, cow dung, butter, rudraksha seeds, ashes, sandalwood, darbha grass, a flower garland or molasses.

Various Interpretation of Shiva Linga
Besides regarding Shiva Linga as the symbol and form of Lord Shiva, religious scholars have given various interpretations of Shiva Linga. Here is the brief description of some of the popular theories and interpretations related to Shiva Linga and its origin:

Worship of the Phallus
According to some scholars, worship of Shiva Linga in effect means worship of the reproduction function. For, they say that the other meaning of the Sanskrit word ‘Linga’ is gender in general and phallus (the male reproductive organ) in particular. They believe that the base of the Lingam corresponds to the Yoni which mean vagina or the female reproductive organ. Correspondence of Linga and Yoni in a Shiva Linga is therefore interpreted as the representation of the process of copulation. Scholars further opine that the Kalash (container of water) that is suspended over the Shiva Linga from which water drips over the Linga also correspond to the idea of intercourse.

Connecting the origin of Shiva Linga to the early Indus Valley civilization, scholars opine that tribes of the Indus Valley took to the togetherness of Lingam and Yoni in a Shiva Linga as the point of energy, creation and enlightenment.

Interpretation in Tantra
According to Tantra, Lingam is a symbol of Shiva's phallus in spiritual form. They say, the lingam contains the soul-seed within which lies the essence of the entire cosmos. The lingam arises out of the base (Yoni) which represents Parvati according to some or Vishnu, Brahma in female and neuter form according to others.

Interpretation in Puranas
Puranas, especially the Vamana Purana, Shiva Purana, Linga Purana, Skanda Purana, Matsya Purana and Visva-Sara-Prakasha attribute the origin of Shiva Linga to the curse of sages leading to the separation of and installation of the phallus of Lord Shiva on earth. Some also refer to the endlessness of the lingam to be linked to the egos of Lord Vishnu and Lord Brahma.

Interpretation of Shiva Linga as an Abstract Symbol of God
Some scholars of the Hindu scriptures say that Linga is merely an abstract symbol of the God. They point towards several legends in Hinduism where a sundry rock or even a pile of sand has been used by as a Lingam or the symbol of Shiva. Citing a particular instance they say, Arjuna once fashioned a linga of clay when worshipping Shiva. Scholars of Puranas, thus argue that too much should not be made of the usual shape of the Lingam. Scholars say that the interpretation of Shiva Linga as an abstract form of God is also consonant with philosophies that hold that God may be conceptualized and worshipped in any convenient form. The form itself is irrelevant, as the divine power that it represents is all that matters. Scholars thus say that Sivalinga represent the formless Nirguna Brahman or the formless Supreme Being.