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.