1. The use by guess or cookbook of an obscure or hairy system, feature, or algorithm that one does not truly understand. The implication is that the technique may not work, and if it doesn’t, one will never know why..
2. Things programmers do that they know shouldn’t work but they try anyway, and which sometimes actually work, such as recompiling everything.

http://www.science.uva.nl/~mes/jargon/v/voodooprogramming.html