Hello Grace, The 'floor length' one will just cover your feet and touch the floor ,while the 'sweep' one will be longer and part of it will be sweeping the floor behind you when you walk. Check those images to see the difference: A sweep dress: http://www.ybridal.com/catalog/product/gallery/id/3228/image/11536/ A floor length one: http://www.lightinthebox.com/index.php?main_page=popup_larger_image&num=0&products_id=26923

A floor length train is really not a train, because the fabric only nearly touches the floor. The hemline will be the same height in the front and back. A sweeping train is a short train, also called a brush train because it just brushes the floor. Usually, the back hem is only a few inches lower then the front hem. As you walk, it would drag on the floor.