A DVD with two data layers on one side. DVD-9 media have nearly twice as much storage as a regular DVD disc (8.5 vs. 4.7GB). DVD-R DL (DVD-R9) typically uses the "dual" layer designation, while DVD+R DL (DVD+R9) uses "double" layer. However, both dual and double layer designations are used synonymously. See
DVD-5 and
DVD storage capacities.