The silhouette is the outside shape of an object against the background, especially when it is filled in with a solid color.
Here, for example, is an illustration by Barbara Bradley turned into a silhouette. The silhouette by itself still communicates the idea of a girl beside a chair holding up a piece of cloth.
Here's the illustration in full color.
The silhouette helps us to immediately recognize animals, plants, or figures. It's a great way to sketch, and you can do it conveniently with a black brushpen. These are some sketches I did of tree silhouettes in southern California.
The silhouette conveys essential information about the mood and action of the pose. By carefully considering the silhouette, you can give your design more impact.
A face in profile is a common kind of silhouette. In the old days you could get a cheap portrait cut from black paper by a skilled artist.
The character Uncle Doodle is shown as he appeared in Dinotopia: The World Beneath.
Here is the same figure converted to a black silhouette. The whole pose, including the face and both hands, is clear enough from the silhouette alone. This kind of broad comic posing suggests pantomime stage acting from the Vaudeville era, and was popular with golden age American Illustrators, especially Maxfield Parrish, J.C. Leyendecker, and Norman Rockwell.
Thanks Leif Peng for the Bradley, link.
Tomorrow: More on silhouette