The name comes from Duffel, a town in Belgium where the thick cloth used to make the bag originated. More recently, a duffel bag typically refers to the specific style of bag, though the phrase may also be used to refer to any large generic holdall or a bag made of thick fabric.
It is often used to carry luggage or sports equipment by people who travel in the outdoors. Duffel bags are also often used by military personnel. When used by sailors, they are sometimes called seabags in this capacity.