When you move or paste a selection, some of the pixels surrounding the selection border are included with the selection. These extra pixels can result in a fringe or halo around the edges of the selection. The Defringe Layer command replaces the color of any fringe pixels with the colors of nearby pixels containing pure colors (those without background color). For example, if you select a yellow object on a blue background and then move the selection, some of the blue background is moved with the object. Defringe Layer replaces the blue pixels with yellow pixels.