Images without colour information, displayed only in black, white and varying shades of gray.
A grayscale image does not contain any colour information and is displayed only in black, white and shades of gray. For raster images, this is a separate 'colour' setting.
Since there is way less information to be stored per pixel compared to a colour image, image file formats may have a separate setting for grayscale images to save storage space.
Questions with this tag should involve the use, creation or editing of grayscale images, or converting to or from grayscale.