What does biting your lip mean?

I've read a few places and a few posts (if memory serves) where it says lip biting is a good sign when with a girl. Yesterday I was with my friends girlfriend that I have a crush on and she was constantly biting her lip (not like every second but very often) and she told me a story about how when she had her last boyfriend before my friend she liked this guy but had to turn him down because she was going out with him etc...is this because we are friends or because she might be attracted to me. Not that I would cheat on my friend with her, god forbid.

Also this girl I was with today thats pretty, pretty funny and pretty shy (factor it out and you get pretty(1 + funny + shy)). She also bit her lip a bunch of times, not as many as the other but I started to notice though. She said something and smiled and I commented back and she bit her lip and smiled.

Anyway for all I know girls that bite there lips could do it because it's a habit I never noticed before. Although I must say I do see the girl bite her lip usually when shes with my friend.

regarding body language, it means she's trying to redden her lips and make them appear fuller to attract someone (probably you) ... full red lips are a sexual signal, which explains the invention of lipstick and collagen injections.
She may not realise she's doing it, and she probably doesn't realise WHY she's doing. It's also a way of flirting.

However, if she doesn't seem happy when she does it it could also be a sign of anxiety.

oooh thanks missleepy. i was thinking lip biting while kissing.

I wouldn't take lip-biting as anything more than a habit without some other clues that she is interested. Some people are just fidgety.