Shorthand for "duffle bag", which is or was a heavy canvas bag, ugly green in color, in which soldiers carried all their worldly possessions, or at least the crap they didn't immediately need. Also known to the Navy and Marines as a "sea bag." The top folded over in quarters onto a loop of metal and the strap clipped to the loop (that was also where you put a padlock). There was also a carrying handle. Your name and serial number were stenciled on the side. Newer models also had/have a back-pack straps arrangement. If you see a picture of GIs "shipping out" who are carrying heavy bags on their shoulders, those are duffle bags.

One of the nastier things Those In Charge could do as punishment would be to give an offending squad or platoon 30 minutes to pack up their duffle bags and fall out for inspection in fatigue clothing. Then you give them another 30 minutes to unpack and be ready for an inspection in the barracks in Class A uniform. Then you change it to an inspection of their full field kit 30 minutes later. Because nobody can get themselves, their equipment, and their barracks ready for inspection in 30 minutes you could find "good reasons" to put the entire group on restriction and extra cleaning duty until they passed your inspection. As a Platoon Sergeant and Acting Platoon Leader (no officer available) I would NEVER have even thought of doing such a thing, much less doing it.

What we have coming is made of heavy-duty nylon, with wheels, and is about 30 inches long with a side-opening zipper. The entire unit weighs about a quarter or less of the ol' original duffle bag. Briefly, it's a big bag with a set of wheels.