Śiva, the third deity of the Hindu Trinity responsible for the dissolution of this universe is worshipped both in the anthropomorphic aspect and as the liṅga. The latter however is the rule, the former being an exception. Etymologically the word ‘liṅga’ stands for that in which everything gets dissolved (līyate asmin iti liṅgaḥ). Liṅga also means an emblem. Hence the Śivaliṅga is an emblem of God Śiva into whom everything gets dissolved at the time of destruction of the created universe. Since God is beyond name and form and since we cannot conceive of an abstract principle like Him without the aid of concrete symbols, a rounded surface is perhaps the nearest approach to him.
Śivaliṅgas may be cala (movable) or acala (immovable). The acala-liṅgas, also called sthāvara-liṅgas, are the stone liṅgas permanently fixed in the temples. There are several varieties of them classified under four or six or even nine groups. An acalaliṅga has three parts: Brahmabhāga (square in shape), Viṣṇubhāga (octagonal) and Rudrabhāga (round). The first two parts are embedded inside the pedestal, the third part alone being visible. This is the one to which pūjā or worship is offered. Hence it is called the ‘pūjābhāga.’