I found this on the internet, it does not say much. What I get from this is that if it's quilted or tied, it's still a quilt.
A quilt is a thick embroidered blanket/comforter, usually in a checkered pattern with raised designs.
A comforter is a thick, quilted, fluffy blanket. Sometimes it’s decorated and colored, but with dye, not embroidered like a quilt. It is usually filled with a synthetic fiber filler. It does not need a cover and is made to be the bedspread. It is usually washed when it gets dirty.
A bedspread is a pre-filled bed cover with stuffing to be used as a decorative and warming bed covering. Normally used as the top cover on your bed. Bedspreads do not require a duvet, duvet cover, or a comforter.
A duvet is a comforter that is filled with down feathers. The duvet is usually white, beige or off-white. It should be placed in a duvet cover. It can be made of down or polyfill.
A duvet cover covers a duvet--like a slip on decorator. Most duvets are not decorated and usually people buy duvet covers. Imagine the duvet as a big flat pillow and the duvet cover as a big pillowcase. They keep the down clean and you can change the color of your bed on a moment’s whim.
As a duvet has a cover around it, it is usually not washed as it does not get dirty. The duvet cover is put in the laundry as a comforter would be. The fact the duvet is not washed means that natural materials (like down) can be used as insulation, which otherwise could be 'damaged' by laundering.