This is the back part of the knee on men or women. Also known as the "Legendary Fourth Hole" in women. You can only see the dinkus from exactly the right angle much like the entrance to Hogwarts.
Multiple: Dinkii, (dink-eye)
Dude, I've got massive dinkus sweat...
Man 1: What'd you do last night?
Man 2: I did this chick in the dinkus last night. Hands down best sexual experience of my life.