Silhouette are terms from painting, optics, photography. They are used to describe the outline or contour of a surface or the area enclosed by this contour, which stands out darkly against a light background (or vice versa). This can also be a natural contour (for example, the shadow of a body or the contour of a city (skyline) created by building development) or an artificial one (for example, a shadow drawing or silhouette).

This is how the term "silhouette" is explained in wikipedia. I like such photos, even if they are quite easy to realize. A bright background and a motif, which can be transformed into a silhouette by selective underexposure. But that's exactly how it works the other way around! A dark background and an illuminated subject in the foreground.  But you can also create silhouettes only in a part of the photo. So there is enough leeway to be creative...