Magic is a metaphysical force that is both part of and transcends the physical world. There are those who work with this power for the benefit of people and nature such as the Cut-Wife. There are also those who use the magical arts not only for their own ends but to serve the powers of darkness.
Magic in the Ancient World
Whilst belief in magic somewhat reduced over time, magic in the old world had a much more common place. From the magicians priests of ancient Egypt to the necromancers of Babylon. There may indeed by many approaches to magic.
The Cut-wife explains to Vanessa how she was once with her sister witches a healer and herbalist and continues to use her craft for such things. She elaborates on how the darker powers seduced witches with more power for their souls and service. Though it seems spells were always something they were capable of it is something taken very seriously and with wisdom.
Spells
A spell is a ritual actions made by someone usually connected to power either innately, through study or through the use of magical items to produce magical effects. Incantations being words that breathe life into the spell and intention of the occultist.
Verbis Diablo
The main language of spells seems to be the Verbis Diablo, the language of the devil which pierces reality and alters is for the spell caster. Though it can be used for good or bad effects its tainted by darkness. The Cut-Wife warns Vanessa Ives that she must use spells sparingly as using the Verbis Dablo could mean you don't stop speaking the devil's tongue and soon it wont be you speaking at all but the powers of hell.