A portrait of a person in profile showing the outline only, usually cut out of black paper and placed against a white ground. Silhouettes were a popular form of portraiture in the 18th and 19th centuries, but declined with the advent of photography. In recent years  some contemporary artists, such as Kara Walker and William Kentridge, have incorporated silhouettes into their work. Web resource here.

Silhouette of a woman, possibly Louisa Wylie Boisen, in a gold oval frame. Ca. 1880-1890. Wylie House, Indiana University, Bloomington, IN.