How do you call the blanket that one uses to cover oneself in bed with, like is there a general term used? (if you could add also your region that'd be superb)

Question

Answer

In the U.S., the topmost thicker blanket is commonly called a bedspread, or a quilt. You won't hear duvet as much, but comforter is another common term. The lower blankets are just called blankets.

Answer

In the UK we call this a "duvet".

In olden times (50+ 
years ago) when people used blankets and sheets to cover themselves in bed, on the top of the blankets people would have an "eiderdown". Traditionally this was filled with feathers from the eider duck.

Answer

American here.
We often use "a blanket" as a general term.
"A quilt" if it is "quilted."
"A comforter" if the blanket has more than one layer and insulation inside.

Good luck!