A Diablo II Open Server means that your character is not stored on PvPGN like on the real Battle.net (TM). When you play on Battle.net (TM), your player is stored on their server. In Open Battle.net (TM) game play, your character is stored on your local computer instead. This only requires PvPGN to be running on the server side. It has several advantages & disadvantages. You may run both an open & closed server at the same time. The player, in such a situation, would then choose which game play they would like to use (open or closed).