A vignette is a dark or light border around the edges or selected portions of a photographic image. Photographers and retouchers apply them in order to direct viewers' attention or help keep a viewer's eyes centered in the frame.
In this 'Sorta Short' series video I demonstrate how to use Photoshop's Elliptical and Rectangular Marquee tools, modify vignette selections, work with masks, an Exposure layer and (optionally) a Hue/Saturation layer to add vignettes to images.