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]

WordNet (r) 3.0 (2006):

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

The Jargon File (version 4.4.7, 29 Dec 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.


The Free On-line Dictionary of Computing (30 December 2018):

lurking
lurk
lurker

    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)