Webster’s defines witchcraft as the act or instance of employing sorcery, especially with malevolent intent: a magical rite or technique. Witchcraft calls upon the powers of the devil much like a believer prays and believes in the power of God.
Witchcraft is also the prefered medium to get in touch with ghosts and lesser spirits.
Disclaimer: most of this site deals with the superstition and folklore that was attached to witchcraft before modern time. Wiccans and neo-pagans, please take no offense as you are not concerned.