On web sites it's people who frequent the site but never post. They usually frequent the site because of great information or for sale ads.
I believe that in most of the contexts used here it is someone that is not a member, but does a lot of reading on the site. I would surmise that many of us were lurkers before joining.
FCBO use to be heavy with leads and ads to C-bodies with expert condition and value evaluations. The lurkers were heavy and grabbed the cars we talked about and most of them were flippers looking to make an easy buck from our evaluations. Not so much anymore....so a lot of the lurkers left. You can tell when there was 200 people viewing FCBO and only 20 of them were FCBO members.
We were on to them and told our FCBO members not to post the ad until after arrangements were made to buy the car so the lurkers wouldn't be able to snag the car. We PM'd the ad and info to members who were interested in some stunning cars or parts in the past.
I won't use the meme because it piss's Big John off! You need to be a grown up and find things out yourself! https://duckduckgo.com/?q=lurker+definition&t=h_&ia=definition
They are not here anymore because they starved to death trying to make a living by flipping C-bodies.
Ya know it's really unfortunate how the world has changed, for the worse IMHO, the PC and women's lib, me too crap, has really ruined things. Back in the day, girls were flattered if you took the time to find out more about them, where they worked, what they drove etc. Things like harmless flirting, or to leave a flower on their car or go to where they work and offer to take them for coffee. Now.... your harassing and stalking them. I'm so glad I'm not growing up in this era and good luck to those who are.