Spirit Magic is a powerful form of witchcraft that called upon the aid of the "The Spirits". It was commonly used among witches as it was considered a major source of power. Since witches are the servants of Nature, and their purpose is to maintain the balance, they used the power that the Spirits provide by calling out to them which has usually been done by accessing a place marked with power.
Since the destruction of the Other Side and the Spirits' forced departure from the now-destroyed dimension in Home, this form of magic is, seemingly, no longer practiced. However, as of I Was Feeling Epic, the spirits of deceased witches that have found peace are still be able to practice magic, even from the Afterlife. It remains unclear if mortal witches can access this magic, effectively tapping back into spirit magic, since those spirits reside beyond known bounds.