After some googling, this is what I found:
Lilith is not made up out of anything material. It is symbolic.
Imagine the elipse that the orbit of the moon creates. Since it is an elipse, it has two 'focal points'. Earth occupies one of them, the other is an empty point. This point revolves around the earth roughly once every 9 years due to variations in Lunas orbit.
This empty point has symbolic meaning; It counterbalances our bright Luna. It represents on one hand repressed feelings and desires, but also letting yourself go and doing things you are usually afraid to do.
The name comes from a Babylonian/Syrian demon-godess who is represented by the glyph of a dark moon.
I derived this mainly from the website
Lilith - the dark moon - Astrodienst . It also includes a good illustration.
[This message has been edited by Melchior, 02-24-2004]
[This message has been edited by Melchior, 02-24-2004]