Usually, "open" means the answer to a question is open, i.e. there's not enough information to give a specific answer. It could also have other meanings (for example the questioner should be more open, etc.) as the C's answers tend to have multiple layers of meanings and hints. "Close" is mostly used as "almost."
Since this is your first post, it is recommended that new members post an introduction in the Newbies forum http://cassiopaea.org/forum/index.php/board,39.0.html telling how they found their way here and how much of the material they've read, etc. Welcome to the forum. :)