Long Edge Binding means the finished book is a portrait. Short Edge binding means the finished book will be landscape. So for example, assume you have a 5.5" x 8.5" booklet. With long-edge binding, the flat side of the booklet will be 8.5" x 11" and the binding will occur on the 8.5" side. With short-edge binding, the flat side of the booklet will be 5.5" x 17" and the binding will occur on the 5.5" side.