In Witchcraft and Wicca in particular the cauldron is a pot, usually cast iron, that is used as the focal point of rituals. It is considered to be the vessel were magical transformations occur and thus is associated with such magical concepts as the Holy Grail, the sacred spring of life, and the primeval sea of creation. It is one of the symbols of The Goddess and hence, symbolic of the manifested essence of feminine energies and fertility. Additionally the cauldron is symbolic of inspiration, the element of water, rebirth, immorality, and ultimately of witchcraft itself. 
The Irish legends of Cerridwen's Cauldron are the source of much lore surrounding the cauldron in contemporary Wicca and Witchcraft.
 Cunningham, Scott, Wicca: A Guide for the Solitary Practitioner, Saint Paul, MN: Llewellyn Publications, 1988. [ISBN 0-87542-118-0 (PB)]