lurker
lurker: n. One of the `silent majority' in a 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.