Grey magic is magick that is neither White Magick nor Black Magick. Grey Magick is neutral in deffiniton though the spells involved tend to sway between either outcome. The most widely used saying used by Grey Witches/Wizards is "There are no sides only choices."
With Grey Magick the spells no matter the casters intent can go either way. For Example If you're casting a money spell to erase debt it's a 50-50 possibility that the spell might turn negative on you and back fire or vise-vresa.