The ability to be passable, to not be mistaken for another gender/sex. When you have passability it means that you are passable as the gender you perform. If you are atransgender woman and no one ever mistakes you for a man, then you have passability as a woman.
"All of these are passabilities, Gorgee, you should know better thanpresenting this nonsense to your boss," says Karen. "S-sorry mistress," Gorgee stutters. "How dare yo-," but she was cut off for the titans had returned.