Generally speaking, an outline or profile of a shape or object, commonly filled with a solid color (such as black).
A silhouette halftone is a portion of a halftone image that has been outlined and separated from the surrounding image areas by removing the dots that surround it.
In digital imaging, in particular on color electronic publishing systems, silhouette refers to a function that allows the isolation of a particular area of an image for local correction or other image manipulation. Silhouettes can be created on these systems when the desired area differs significantly in density from the surrounding image areas.