Refutation of the initial answer: it hides much more than it reveals and therefore cannot (really) be called “Gilui” (2).
Three rules of “Etzem” and Gilui.
Every Tzimtzum is two Tzimtzums:
1) removing the Ohr Haoleh AL Kulana.
2) Miut (hischalkus) of the Chitzoniyus HaOhr. MP3
