Where one voids his or her bowels, only to find, by wiping one's anus, that no evidence of the event remains. Not as rare as immaculate conception, but still magical.
Cletus found, after taking a huge shit, that his first wipe was completely clean. "Hallelujah!" He exlaimed, "Immaculatedefecation!"
The holy grail of bowel movements. You take a big ol' dump, and you wipe. Then you look and see that thetoilet paper is clean, and no turd is in the toilet. So clean, it's almost divine.
The ImmaculateDefecation is the best poop in the world. No turd to clog the toilet, no mess on the TP to worry about. It's like God took the dump for you.
Brad glimpsed at the used toilet paper to gauge his progress and was astonished to be greeted by a wad of pristine, folded two-ply. He struggled to recall his diet that had resulted in this ImmaculateDefecation and knew his friends would not believe him later.
"Yo, where's Jude?"
"He went to take another poop."
"None of us have eaten in the last 24 hours, and we all used the loo before leaving!"
"Bruh, it's an immaculate defacation!"