This most probably refers to the "hole" which is used to insert the insert of the blanket, which, for most people at least, means that it should be at the "feet" end of the bed. It's just some blankets have zippers to cover the hole, others have buttons etc.
I have certainly never been duvet levels of fancy.
United States: Duvets are fancy. Norway: Common, everyday stuff.
We used sleeping bags as blankets growing up because we were weird I guess.
....By the way, you're not weird for using sleeping bags; you're fun! :-)
... I've never seen a blanket with a zipper or buttons...
Usually a bed here is a blanket or comforter, then a top sheet, then a fitted sheet on the mattress. In hotels/motels you'll sometimes see a comforter AND a blanket with the two sheets.
(Based on photos of duvets) I think a comforter is somewhat like a thinner duvet with a non-removable cover.
As someone else said in this thread, when I heard 'blanket' and 'zipper' together the only thing that came to mind was a sleeping bag.
Some folks just aren't bothered by such things.
Or have better focus than I do.
a) What kind of blanket has a zipper? I don’t think I have encountered any.
b) As the kind of person with several thousand unread emails, I don’t know why people bother? I can easily search for the important stuff, and visually scan the new pile a few times a day. I have better things to do with my life than manage my inbox, I don’t need that stress. Family, video games, basically anything else. It’s way more work than reward. I know a number of people this drives absolutely nuts, but I don’t get it.