Magic of a dark nature, that harms or injures a victim, or perhaps requires a sacrifice to increase strength or some other attribute of the caster. Usually calls upon energy from evil or demonic beings. Primarily used by wizards and witches. Also known as the occult, and looked down upon by most religions.
I, however, believe that it is not the spell but the intent behind it that determines the ethics of the spell. I also do believe that it is entirely fictional. Contrast with White Magic.