The fourth hole of a woman. Quagmire from the cartoon family guy says its located behind the left knee. In reality , the fourth hole could be referring to a woman's urethra. Although penetration is difficult, it is not impossible.
-Man, I cant believe that Sandy kept it from me for so long! Women have a fourth hole!
-Now you be careful Jimmy. Not every gal you meet is ready for that sort of sex .
Alternatively bound to the saying:
Every hole is a goal
Watch out men..when a woman says you can use all 4 holes, she's referring to your hole as the fourth. She has a secret fetish that she disguises as something good for you only it's not. It's a Jedi mind trick you in the ass.
A phenomenon where a woman has just the right amount of fat on her ass and thighs, that when she stands upright, a fourth fuckble hole is created where the butt cheek and thigh meet.