A lurker is someone that follows the forum but doesn’t post.

People who look at your myspace and dont leave comments, messages, pic comments, etc.

someone who seems to always be present bu unnoticed

People who go on your stickam profile when your live and dont come into the chat.

one who reads a blog without ever commenting on the posts

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.

A lurker is someone who always just seems to be there, no matter where it is.

You always expect them to be there, because they pop up out of no where.

A lurker will often try and play it off as a joke when you confront them, but it's not a joke.