The term lurker has been around as long as forums (and newsgroups). It basically means someone who just reads the discussions but doesn't respond or take a more active role in the discussion. There isn't anything negative to it.
Many folks still abide by the unwritten rule taught to them when they were children; "If you don't have anything nice to say, don't say anything at all."
I don't mean that they would say something negative in a thread, but that they don't have anything to add to the discussion so they stay silent.
In the early days of this forum, someone would ask a question and the first half dozen posts would all be something like, "Wait til (___) reads this; he's an expert and will have the answer."
I think it was a way to assure the original poster that he wasn't being ignored and that he asked the question in the right place and that there would be someone along who might know the answer.
I know in some of the eariest modeling forums (back in the 90s), many first time posters (and new to the world wide web) thought it was like 24/7 online help. They'd post a question or say hello and then 5 minutes later wonder why it wasn't answered. They'd post three of four more times in a span of 10 minutes, eventually get discouraged and leave in disgust. It was kind of funny and sad at the same time.