This is the point of contact from the coxix tho the anus of one's buttocks. As the buttocks can be spread apart, the contact forms a 'crease'. This crease in in one's buttocks is known as the 'Batty Crease'. It is a colloquialism that can be used as a noun or an adjective.

A pubic hair piece. A toupee for the pubic area/genitals. In the 1700’s when mercury was used to treat sexually transmitted diseases (Gonorrhea or Syphilis) one of the side effects was the loss of pubic hair. To disguise this condition, that was not cured by mercury, a Merkin was employed.

The point at which ones thighs meet at the back of the body, usually referred to as the buttocks. The "batty crease" is therefore the crack in ones buttocks

a creasing of the anus after exessive boneing

The most unsensitive part of the body situated on the back above the legs below the spine. It is unsensitve unless your attacked by the sh*ts

The process used in the creasing of one's batty.