Source: Prachur

Many believe that “LINGA” means male reproductive organ and Shiva Lingam is ‘Phallus’, the symbol of generative power in nature.But this is a wrong assumption even by many Hindus due to their ignorance and lack of understanding sanskrit.Infact “SISNA” is correct sanskrit word for male phallus and not Lingam.Over many years, ignorance and misinterpretations made many believe that Lingam means ‘Phallus’.

Siva Purana describes formation of Lingam as a pillar of light for which top and bottom were never found.The night when this pillar of light appeared is celebrated as Mahasivaratri.

Siva Linga consists of 3 parts:
Lowest of which is called the “Brahma-Pitha” which creates the universe,
Middle one is the “Vishnu-Pitha” which preserves the creation, and 
Uppermost one, the “Siva-Pitha” which destroys or absorbs everything back into itself.

Linga is shaped like an egg, and represents the ‘Brahmanda‘ or the cosmic egg.It signifies that the creation is effected by the union of ‘Prakriti‘ and ‘Purusha,’ the male and the female powers of Nature