Slender straight heel. Closed, slightly pointed toe. Without straps or decorations. Vamps that don't show much toe cleavage. Sides cut fairly high.
Opera pumps are usually black patent or black kidskin.
Just think of your typical representaion of a fetish shoe and you've got it. A classically designed shoe originating in Oxford, England. It's a cheaters way to have very high heels. Can sometime also be toeless. There are also open-toed pumps which have the end of the toe box cut out so the toes show.