The lingam (also, linga, ling, Shiva linga, Shiv ling, Sanskrit लिङ्गं, liṅgaṃ, meaning “mark”, “sign”, “gender”, “phallus”, “inference” or “eternal procreative germ” is a representation of the Hindu deity Shiva used for worship in temples. Whether the lingam symbolizes the physical body of the god or something purely spiritual is the topic of many a century-old debate within Hinduism.

The lingam is often represented with the yoni, a symbol of the goddess or of Shakti, female creative energy. The union of lingam and yoni represents the “indivisible two-in-oneness of male and female, the passive space and active time from which all life originates”. The lingam and the yoni have been interpreted as the male and female sexual organs since the end of the 19th century by some scholars, while to practising Hindus they stand for the inseparability of the male and female principles and the totality of creation.

http://en.wikipedia.org/wiki/Lingam