When your balls sweat profusely and it's been a few days since you've showered so all the lint, dead skin cells, and sweat accumulate into a fine butter on your scrotum. Often used as a lubricant for anal.
"Don't forget to scrape off your scrotum butter with a butter knife before going to grandma's, sweetie"
by CrispyFetus January 15, 2019
The substance that accumulates when wiping your ass from back to front. Similar to peanut butter in appearance.
by Spazz March 16, 2004