The distinctive imprint pattern left on bed sheets after a particularly sweaty encounter, formed typically by the back/underside of the male participant.
Like the actual Turin Shroud, but not involving Jesus...probably.
..."better throw the covers back over, don't want your mother seeing the Turin Shroud!"
Named after the famous burial cloth. The shroud of turin is made with a paper napkin or paper towel. If you have a sweaty, dirty ass you reach back and clean it up with the paper towel or napkin. Then you place it over the face of someone while they are sleeping, hence the shroud of turin.
The act of ejaculating onto a wash cloth and placing it on a persons face while they are sleeping. Once it hardens, it should have an imprint of their face.