A person who is just "there." Nobody really knows why, other than they show up and don't say a word. Possible reasons for this could be:
-They don't know what to say
-They are pretending to have friends
-They are trying to scare you
-They are there just to be seen with you, as if they have some kind of relationship with you.
Person 1: Who's that?
Person 2: The lurker. He shows up everyday, just ignore him.