[poss. from C. S. Lewis's Narnia books] An
awesomely arcane technique central to a program or system, esp. one
neither generally published nor available to hackers at large (compare
black art); one that could only have been composed
by a true wizard. Compiler optimization techniques
and many aspects of OS design used to be
deep magic; many techniques in cryptography, signal
processing, graphics, and AI still are. Compare
heavy wizardry. Esp.: found in comments of the form Deep
magic begins here...
. Compare
voodoo programming.