(a)
The line which marks the outer limits of an object or figure; the exterior line or edge; contour.
(b)
In art: A line drawn by pencil, pen, graver, or the like, by which the boundary of a figure is indicated.
(c)
A sketch composed of such lines; the delineation of a figure without shading. "Painters, by their outlines, colors, lights, and shadows, represent the same in their pictures."