A duvet is a large stuffed inside pouch that goes inside a duvet cover to provide a nice, warm cover for a bed. The advantages of the duvet and cover system is that the cover can be removed and thrown in the wash or a different cover can be used to change the appearance easily and more cheaply than buying a new comforter or blanket and coverlet. A disadvantage is that it's harder to adjust the layers and amount of warmth provided than it is with some other covers.
Duvet use is more common in Europe than in North America. Other regions?
The stuffing in a duvet can be
The cover can be any fabric, commonly,