I suppose it should be on the documentation. As far as i'm aware all that does is remove topics from that category from the discussion listing so you're not over cluttered with things that dont interest you if you dont want to be. If that makes sense.
:) Technically it can be changed on the dictionary for those who it bugs (no pun intended). But i suppose to avoid future confusion it should be changed properly.
well if you hover over 'block user' it gives you an alt saying so. I guess saying block html would be more understandable but also more clutter. tough compromise.