The term "vignette" refers to the darkening of edges in an image. Sometimes this occurs unintentionally from lens characteristics when taking a picture. Using Capture NX 2, you can use Vignette Control to brighten up those edges.

Note: Vignette Control can only be applied to image data that was captured with a Nikon D-SLR, and is particularly effective with images taken using a D/G-type NIKKOR lens.