The inexplicable force in some girls that causes them to grind on nearby objects (poles, girls, guys, animals). Located in the hiney
or in rare cases the crotch.
John: Damn Gwen, turn down the Grind Magnet, you just traumatized the nurses at the convelescent home!
Gwen (while Grinding on John): I know, i can't help it! It never turns off!