The disgusting, smelly residue left over after a long day of farting on the anus and inner buttcheeks. Aside from the wet feeling, usually is not made apparent until the buttcheeks are spread, releasing the smell. Also can be caused by poor wiping.
"Oh man, I was pounding this broad from the bar and my toot goop was making this hideous smell. I can't believe she didn't smell it!"