1) A girl/woman who doesn't like being on the
bottom, typically because they
don't enjoy being "dominated". I'm also told the
bottom hurts more; that might be another reason (although I wouldn't know).
2) A woman who does not want to be submissive to
men. It comes from the old Hebrew story of Lilith, who was Adam's first wife. She was forbidden to live in the Garden of Eden because she refused to be secondary to Adam. The term 'Lilith' generally has a very negative connotation, and is often associated with feminism.
"Hey bro, are you still
dating *insert girl's name here*? "
"Nah, I had to break it off. She was a
total Lilith; I
just couldn't take it anymore. "