A lurker is the female version of a creeper. Lurkers are girls that are weird, odd, or anti-social. They almost never like attention on themselves, and are usually creepily quiet. They can sometimes be stalkers.
'Look at that lurker...'
'Yeah, she's been around quiet a bit lately.'
A guy that is weird. He is usually quite out of the ordinary, in both the way he speaks and the way he looks. He usually doesn't have very many friends, and is always in the backround when something happens.