Swami Sivananda, said that in Sanskrit,“the linga means a mark”. It is a symbol which points to an inference. When you see a big flood in a river, you infer that there had been heavy rains the previous day. When you see smoke, you infer that there is fire. This vast world of countless forms is a Linga of the omnipotent Lord. The Siva-Linga is a symbol of Lord Siva. When you look at the Linga, your mind is at once elevated and you begin to think of the Lord.
In his book Hindu Dharma, Bansi Pandit said that the word linga is derived from the two Sanskrit words laya (dissolution) and agaman (recreation). Thus, shivalinga symbolizes that entity in which the creation merges at the time of dissolution and out of which the universe reappears at the beginning of the new cycle of creation."
Shivling (6543m) is also a mountain in Uttaranchal (the Garwhal region of Himalayas). It arises as a sheer pyramid above the snout of the Gangotri Glacier. The mountain resembles a shivling when viewed from certain angles, especially when travelling or trekking from Gangotri to Gomukh as a part of a traditional Hindu pilgrimage.
The word is first attested in the Brahmanas, with general meanings of "sign, mark, characteristic" . Its etymology is uncertain, although related to Sanskrit langala for a plough derived ultimately from a Munda word. It is also related to Proto-Dravidian nan-kol for a plough. Suggestions also include Germanic *leik (English alike) as a cognate.
Various interpretations on the origin and symbolism of the Shiva lingam obtain. While the Tantras and Puranas deem the Shiva lingam a phallic symbol representing the regenerative aspect of the material universe, the Agamas and Shastras do not elaborate on this interpretation, and the Vedas do not mention the Lingam. It's gravest misinterpretation is to relate it to only phallic symbol by its shape more so by western philosophers.
Lingam as a symbol of creation
Hinduism conceptualizes Brahman, the supreme power, as having three main roles: that of GOD the Generator, Organizer and Destroyer. This trinity is represented iconically by the deities Brahma, Vishnu and Shiva respectively. Thus, it is Shiva, the destructive form of the Almighty, who is represented by the Lingam or Mark, which is manifestly the CREATIVE power of Divinity. This points to an origin of the tradition of using the Lingam as a divine symbol that is utterly sublime Light(Jyoti) in its philosophical underpinnings.
Lingam as an abstract symbol of God
Some knowledgeable interpreters of Hindu scripture believe the lingam to be merely an abstract symbol, and point out that Lingams in many of the more important temples are not of the shape described above. Furthermore, many are the instances in Hindu lore where a sundry rock or pile of sand has been used by heroic personages as a Lingam or symbol of Shiva. For example, Arjuna fashioned a lingam of clay when worshipping Shiva. Thus, it is argued, too much should not be made of the usual shape of the Lingam. This view is also consonant with philosophies that hold that God may be conceptualized and worshipped in any convenient form; the form itself is irrelevant, the divine power that it represents is all that matters.