Simply speaking a pinup is a picture, usually of a female, that appeals to 'popular culture' and which is 'pinned up' somewhere, like a wall or locker door. The word 'pinup' entered popular language during World War II which is when commercial pinup posters started being produced. It was particularly popular among British Forces during World War I, when the craze was for collecting and pinning up publicity postcards of actresses, singers and models of the day.