Vāhana

refers to the being used by a deity as a mount (vehicle). The term is derived from the Sanskrit “Vāh” meaning to carry or to transport. Gods always have an animal asvāhana, sometimes real, sometimes mythical, and sometimes a composite being such as “makara” with attributes of an elephant, a crocodile and a fish.
The famous vehicle of the God Śiva, is called Nandi or Nandin, the joyous, the white Bull.