[Tarana]

I call them all cases. Your delineation only describes how each case works. No, not all 'enclosed' cases are hard. Lots of different materials, some spongy, some quilted, as well as plastic or metal.

I have a sleeve for my Kindle in my purse to protect it from car keys and such. I have a leather like case for my Kindle HD because the thing is heavy and I was afraid of dropping it. The case gives me a better grip, but unfortunately, it is heavier than my ereaders. I mostly use it to play audiobooks and read pdf files now. Anyway, I otherwise do not use a case for the ereaders. One of the advantages of an ereader is that it is lightweight. That said, if I was using my Kindle or Nook for a commute, I'd have a case since chances of dropping it are higher.