In terms of the female anatomy, a crack is also a name for something else. But we won't go there because this clearly isn't the context for it.
Discussion on cracks on the SI Forums is rather limited for a number of reasons. Incidentally, it's probably the same reason as why
Falun Gong isn't widely discussed in China. Although I'm not sure what the exact link is between Marc Vaughan and a spiritualist movement on the other side of the world.
Cracks are like a vacuum cleaner, sucking the food (or, in GK's case, Pot Noodle) from the mouths of developers.
Best piece of advice next time you want a definition, type "Define:
word/s" in Google. Like "
define: no cd crack".