its that lil flap of skin between your balls and ass, or your pussy and ass everyone has one
It taint ass and it taint pussy

The area between the nutsack and asshole that prevent a man from shitting on his nuts. See durf.

A taint is the stretch of skin found only on women between the pussy and the asshole. The term originated from the phrase "taint an asshole and taint a pussy." In contrast the skin between the scrotum and asshole on a man is referred to as the "gooch" and first known usage is a reference to Bob "the gooch" Guccione the owner/publisher of Penthouse. His employees and acquaintances couldn't quite decide if he was more of an asshole or a dick, a general consensus eventually formed that he was both and "everything in between," hence the gooch.

't aint quite your arse and 't aint quite your bollocks it that bit in between

the perineum - the area betwwen the genitals and anus, male or female, although the term is said to orginate from the saying "It ain't pussy and t'aint ass..."

1. On a man, the area between the sack and the crack
2. On a woman, the area between the giney and the heinie

the spot between the pussy and the asshole

the piece of flesh dividing the asshole from the ballsack.