Shiva’s bull. (Glossary for the Vahinis)

Nandi or the bull seated in the temple, facing lord Shiva signifies the jiva and individual consciousness, which is the vehicle of the divine. When the jiva turns towards god and takes position face to face before him, the same jiva becomes Nandi – one filled with ananda which he radiates to all. (NNSG Vol.7, p. 9)