Hot, but not totally smoking hot. Girls who are sneaky hot are not usually in the conversation of being among the hottest of their group, but when mentioned or seen you remember that they are rather attractive. They are generally better looking in person than on TV or in pictures.
Bill Simmons, aka "The Sports Guy," has created the "Sneaky Hot Hall of Fame" for actresses who look better in person than on TV. Its members include Lauren Graham, Laura Linney, Anne Hathaway, Diane Sawyer, Jamie-Lynn Sigler, and Lori Loughlin.