a very good question. generally Magick (why the k - everyone knows the difference between stage illusions and 'real' magic!) could be anything supernatural - natural magick is meant to work by using the earth's magical field which is related to ley lines, black magic by conjuring demons/spirits and voodoo/healing magic by communing with the dead.
All of these can be summed up in this way: there are forces which normal people can't usually see or experience (let's call them supernatural forces); by a variety of methods (usually mental discipline, learning from other works/people and bodily purification or drug use) the mind can be altered to the extent where visualisation of magical or supernatural forces is possible; control of these forces is usually done through a medium - i.e. the magickian demands, entreats or otherwise arm-bends a goddess, nature spirit, soul or whoever is seemed most relevant to control the supernatural forces for the magickian.
Thus the unknown becomes known and this knowledge leads to control of both the external and internal world of the magickian.
or is that a load of BS?
All of these can be summed up in this way: there are forces which normal people can't usually see or experience (let's call them supernatural forces); by a variety of methods (usually mental discipline, learning from other works/people and bodily purification or drug use) the mind can be altered to the extent where visualisation of magical or supernatural forces is possible; control of these forces is usually done through a medium - i.e. the magickian demands, entreats or otherwise arm-bends a goddess, nature spirit, soul or whoever is seemed most relevant to control the supernatural forces for the magickian.
Thus the unknown becomes known and this knowledge leads to control of both the external and internal world of the magickian.
or is that a load of BS?