wall

wall interj.  [WPI] 1. An indication of confusion, usually spoken
   with a quizzical tone: "Wall??"  2. A request for further
   explication.  Compare {octal forty}.  3. [UNIX, from `write
   all'] v. To send a message to everyone currently logged in,
   esp. with the wall(8) utility.

   It is said that sense 1 came from the idiom `like talking to a
   blank wall'.  It was originally used in situations where, after you
   had carefully answered a question, the questioner stared at you
   blankly, clearly having understood nothing that was explained.  You
   would then throw out a "Hello, wall?" to elicit some sort of
   response from the questioner.  Later, confused questioners began
   voicing "Wall?" themselves.