A pin-up is an attractive man or woman who appears on posters, often wearing very few clothes.  (Image for illustration only from FB page Pin-up Models) British definition says as per Collins: a picture of a sexually attractive person, esp when partially or totally undressed 

A pin-up model is a model whose mass-produced pictures and photographs have wide appeal within the popular culture of a society. Pin-up models are usually glamour models, actresses, and fashion models whose pictures are intended for informal, aesthetic display, such as being pinned onto a wall.