A pin-up model (known as a pin-up girl for a female and less commonly male pin-up for a male) is a model whose mass-produced pictures see widespread appeal as part of popular culture. Pin-up models were variously glamour models, fashion models, or actresses whose pictures were intended for informal display, i.e. meant to be "pinned-up" on a wall, which is the basis for the etymology of the phrase. These pictures are also sometimes known as cheesecake photos. Cheesecake was an American slang word that became a publicly acceptable term for scantily-clad, semi-nude, or nude photos of women because pin-up was considered taboo in the early 20th century.

The term pin-up may refer to drawings, paintings, and other illustrations as well as photographs. The term was first attested to in English in 1941 even though the practice is documented at least back to the 1890s. Pin-up images could be cut out of magazines or newspapers, or they could be on a postcard or lithograph. Such pictures often appear on walls, desks, or calendars. Posters of these types of images were mass-produced and became popular starting from the mid-20th century.

Male pin-ups (known as beefcake) were less common than their female counterparts throughout the 20th century, but they have existed for the same length of time. In particular, pictures of popular male celebrities were targeted at women or girls; examples include James Dean, Jim Morrison, and Fabio.