I have been running home automation systems since the early 90’s and had never come across the term cover. This is a meaningless term. It does not describe what any sensor does and does not indicate if it is a window or a door. The only thing that comes close would be to cover a motion sensor. But that also makes no sense. It is one of the things that should be done away with if you want HA to be accessible to more people.
As I transition into HA I see many things like this that are a bit “geeky” and should be addressed and more important than changing something that is pretty simple to understand like snapshots.
It is going to take a bit of un-geeking things like this to get to a point where new users won’t be put off.
Cover is a word chosen by the Home Assistant team to describe a device platform. It includes many device types such as doors, windows, awnings, blinds, etc… It describes this group of devices quite well as all these things cover an opening.
So it is not meaningless and it does describe the device function.
When I first encountered this word used in Home Assistant I suspected what it was and a 5 second scan of the documents confirmed it.
I suspect the real issue here is that you don’t want to read any documentation and just want understand everything by default. Sorry that is not how life and learning new things works.