Shadowbanning is, to me, banning that results in the user still believing they aren't banned and that their posts appear, to them, to be posted normally. Shadow banning means the user doesn't even know they were banned and still sees their posts being posted as if there has been no change.

They may only notice the difference after they have logged out and then checked to see if their post has actually been posted like normal. It seems insidious, perhaps nefarious was too strong a word. I can see where some people might have earned such a ban, however.