deep magic n.
[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.