Nandi also called Nandikeshvara,Nandishvara,Shalankayana or Thandava Talika is the name of the gate- guardian deity of Kailasa, the abode of Lord Shiva. He is usually depicted as a bull which also serves as the mount (Sanskrit: Vahana) to the god Shiva. According to Saivite tradition, he is considered as the chief guru of eight disciples of Nandinatha Sampradaya - Sanaka, Sanatana, Sanandana, Sanatkumara, Tirumular, Vyagrapada, Patanjali and Sivayoga Muni who were send to eight directions to spread the wisdom of Shaivism.
The word nandi has come from Tamil root word Nandhu means to grow to flourish or to appear which was used to indicate growing fluorished white bulls as well as divine bull nandi.The Sanskrit word nandi (Sanskrit: नन्दि has the meaning of "happy", "joy" and "satisfaction"; also said as the properties of divine guardian of Lord Shiva - Nandi.Almost all Shiva temples display stone images of a seated Nandi, generally facing the main shrine.
However, it is recently documented that the application of the name Nandi to the bull (Sanskrit: vṛṣabha) is infact a development of recent syncretism of different regional beliefs within Saivism.The oldest Saivite texts in Sanskrit, Tamil and other Indian languages, the name Nandi was widely used instead for an anthropomorphic door-keepers of Kailasha rather than his mount.