Bedding is the removable and washable portion of a human sleeping environment.
A bed sheet is a rectangular piece of cloth or linen cotton used to cover a mattress. It is this sheet that one typically lies on. In many areas of the world, a second flat bed sheet is laid on top of the sheet covering the mattress. This is known as a “flat bed sheet” ,and when a top sheet is used, the sheet covering the mattress is known as a “fitted bed sheet”. From linensncurtains.com
A person sleeps between the two bed sheets. Fitted sheets protect the mattress and provide a comfortable surface for the sleeper to lie on. Flat sheet makes your bedding more welcoming, and protects the blanket from getting dirty. In a warmer night, Flat sheet could be enough, without the blanket.
Bed size are differ from country to country. See this for more details
These are common sizes:
Duvet is a soft flat bag traditionally filled with down or feathers, or a combination of both, and used like a blanket.
There are Natural and Synthetic duvets. Natural come from Duck or Goose.
In short: Goose is better than Duck. Down is more quality, lighter and warmer than Feather.
Duvet cover can replace or be used in addition to the flat bed sheet, the top sheet.
Extra Long Staple, ELS, cotton can be woven into softer and more durable fibers than other types of cotton. There are 2 types of cotton that are Long Staple or ELS.
Supima is the promotional organization of the American Pima cotton growers.
Supima can be a certified for its genuineness. There is a cerification for Egyptian cotton too but its not much popular or organised. In another words, people can mix Giza with long staple Indian cotton and usually won’t get caught. But generally speaking, both are almost equal to each other in quality. From Which is better - Supima or Egyptian Cotton?
Pima now is always extra long stable fiber - the cut off point for staple length being 3.5 cm. Egyptian cotton need not always be extra long staple - though historically Egyptian cotton was famous for long staple length. However the American cotton industry did a marketing coup by defining Pima cotton to always be ELS so that it created perception of quality in the market while Egyptian cotton remained a geographical moniker. Both the Egyptian and American cotton suppliers have raised the ante in marketing -while the Americans have now created the trademark Supima to market products used with US Pima cotton, the Egyptians have created the Giza brand as their version of Extra long staple. As per this Giza 45 is the finest quality of cotton anywhere. From What is the difference between Egyptian and Pima cotton?
Higher thread count does not mean better quality. It depends on your choice of preferences, but take minimum of 200.
Love the feel of a cotton button down shirt? Joanna advises a crisp, dense 200 thread count percale. Prefer a silkier sheet? Go for a 300 to 600 cotton satin. If you want lighter sheets, Joanna says, a 400 thread count sheet can be soft and light, while an 800 percale would be soft and dense. The higher the thread count, the more likely multiple-ply thread is used or picks are added, making the fabric denser and heavier. From styleathome.com
It is designed to lie atop a mattress. Made primarily from foam, its function is to provide a layer of comfort and warmth between the user and the mattress. From wikipedia