Kaoru Aoiciid is short for card instance id. It's the id of every copy or instance of a card in a single match. It's not to be confused with nid which stands for node id, which is the id of a card in the database. Multiple copies of a card share the same nid.
nid can be saved and used between multiple matches but ciid cannot. ciid is meaningless except in the current match and may refer to different cards between matches.