A double duvet.A duvet (pronounced /duːveɪ/, from the French duvet /dyvɛ/ "down") or doona is a type of bedding— a soft flat bag traditionally filled with down or feathers, or a combination of both and used on a bed as a blanket. Duvets originally came out of rural Europe and were made from the down feathers of the Eider duck, which is well known for its usefulness as an insulator. In Spain and Latin America is known as edredón.
In Westphalia, an English travel-writer observed with surprise in 1749,
"There is one thing very particular to them, that they do not cover themselves with bed-cloaths, but lay one feather-bed over, and another under. This is comfortable enough in winter, but how they can bear their feather-beds over them in summer, as is generally practised, I cannot conceive." —Thomas Nugent, The Grand Tour 1749, vol II. p66 
Duvets are still commonly used in Europe (especially in northern Europe and Scandinavia where it is the most common form of bed covering), and have become popular throughout the world in the late twentieth century.
Duvets reduce the complexity of making a bed, as it is a single covering instead of the combination of sheets, blankets, and quilts or other bed covers, which is traditional in many parts of the world. The cover is called a "duvet cover" or a "quilt cover".
Nowadays, a duvet is sometimes filled with silk, wool, or artificial fibers (such as polyester batting or other artificial material). It is sometimes confused with a comforter, although comforters go on top of the traditional sheets and blankets and are primarily decorative while duvets are used alone.
In Australia it is called a "Doona", from a trademarked brand name derived from the Old Norse dunn meaning "down feathers". Though still registered to the Tontine company, the name "Doona" has become a generic term for a duvet or down quilt. Originally the term continental quilt was the standard name used across Australia; some regions of Australia still use this term today.
In Danish and Norwegian it is called a dyne, which is pronounced similarly to the Australian name.
In the US, confusion often occurs as the word "duvet" may refer to a comforter cover rather than the down blanket itself. This is how the term is used by several large retailers,
"For those of you enjoying a down comforter, or even just looking for a change for your bedroom, a duvet could be the perfect answer. Since you will be placing your comforter inside the duvet, it is important that the appropriate size be selected."—Bed, Bath and Beyond, Sizing Up Your Bedroom 
The term Duvet Day is used in some countries to describe an allowance of one day a year when you can simply call work and say you're not coming in, even if you don't have holiday booked and you're not ill. This became fashionable in the late 1990s with many larger companies in the USA and the UK.