The Eldar is the name given to those Elves who responded to the summons of the
Valar to leave Middle Earth and dwell in Valinor. But some of them
followed Feonor in his rebellion and returned to Middle Earth in the First
Age. Of these, most were killed in various wars; the only surviving one
that we know of by the time of LotR is Galadriel. I believe Glorfindel
and some others are descendants of Eldar in ME, but I don't have my book (Sil)
with me to check that. Eldar who never left Valinor are still there, of
course.
This is one of the complicated issues that makes it hard to "get" the Sil in
first reading. Stick around and join or follow the chapter discussions of
the Sil starting shortly, and I think a lot of this will be cleared up for
you!
Join TORnsibs for
LotR Symphony at the Hollywood Bowl Sept. 21, 2004! For details, email erather {at} forth {dot} com.