I'm going to help you out with the last two and add three more.
GM - game master, the person that in in charge of the rp and usually the person that made it
open rp - a rp that anyone can enter no matter what
semi-open - a rp where you need to post a character sheet and the GM needs to approve
semi-closed - a rp that is mostly closed but you can still join
closed - a rp were there is no room for anyone else at the time
those are at least the ones you did not have that were used before the forums reset and/or what they meant.