Definition from Wiktionary, the free dictionary
- (idiomatic) Magic derived from evil forces, as distinct from good or benign forces; or magic performed with the intention of doing harm.
Usage notes 
When referring to advanced technology, calling something (plain) magic means that it is not understood, but implies that it can be by those versed in the field. Black magic, on the other hand, implies that few understand it.
Derived terms 
Coordinate terms 
magic derived from evil forces