A lurk link is a link to someone's myspace profile, for the purpose of whoever you are talking to being able to see who you are talking about. This is widely used in instant message conversations and myspace bulletins.
Darin was telling me how saggy this girl was, and I didn't understand until he sent me a lurk link.
dudeman1: Dude this chick is saggy
mandude2: lurk link, dude.
mandude2: sag city, man.