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.