Known as the action of cosplaying (wearing costumes) characters from the opposite sex; it applies to both genders. NOT related in any way with sexual preferences of the people who practices it, in most of the cases.
A guy that wears a Card Captor Sakura costume is doing crossplay.
Crossplaying is when you cosplay someone of the opposite sex. or gender. Now Cosplaying in general is when you dress up in a costume or outfit to be or act like a character. Cosplay literally means Costume Play. Crossplaying goes for both genders. It means, if to say, you were a guy and went to a convention dressed as Mikasa Ackerman, that's crossplaying.