lurker

from WordNet (r) 3.0 (2006)

lurker
    n 1: someone waiting in concealment [syn: {lurker}, {skulker},
         {lurcher}]

from The Collaborative International Dictionary of English v.0.48

Lurker \Lurk"er\, n.
   1. One who lurks.
      [1913 Webster]

   2. A small fishing boat. [Prov. Eng.]
      [1913 Webster]

from Jargon File (4.4.4, 14 Aug 2003)

lurker
 n.

   One of the `silent majority' in an electronic forum; one who posts
   occasionally or not at all but is known to read the group's postings
   regularly. This term is not pejorative and indeed is casually used
   reflexively: "Oh, I'm just lurking." Often used in the lurkers, the
   hypothetical audience for the group's {flamage}-emitting regulars.
   When a lurker speaks up for the first time, this is called delurking.

   The creator of the popular science-fiction TV series Babylon 5 has
   ties to SF fandom and the hacker culture. In that series, the use of
   the term `lurker' for a homeless or displaced person is a conscious
   reference to the jargon term.

from The Free On-line Dictionary of Computing (8 July 2008)

lurking
lurk
lurker

   <messaging, jargon> The activity of one of the "silent
   majority" in a electronic forum such as {Usenet}; posting
   occasionally or not at all but reading the group's postings
   regularly.  This term is not pejorative and indeed is casually
   used reflexively: "Oh, I'm just lurking".  Often used in "the
   lurkers", the hypothetical audience for the group's
   {flamage}-emitting regulars.

   Lurking and reading the {FAQ} are recommended {netiquette} for
   beginners who need to learn the history and practises of the
   group before posting.

   (1997-06-14)