Wicca is a neo-Pagan religion, founded by Gerald Gerdner, approximatly in 1951. Wicca is polytheistic and is based on the worship of the cycles of Nature and the living things there-in.
There are different sects of Wicca, including Eclectic and Faery Wicca.
Often associated with witchcraft, Wiccans may practice certain magicks in their religious rites, but practicing Wicca is no more synonymous with being a witch, as practicing Christianity.
Living Wicca: A Guide For The Solitary Practitioner, by Scott Cunningham (1993, Llewllyn Publications, St. Paul MN)