A fanlisting is a web clique listing fans of a particular subject. In the case of manga fanlisting, they focus on a specific manga and related content (specific manga-ka, characters,even chapters!).
I do remember seeing similar icons and sites like these when I was younger but never had the motivation to join any. That has since changed, clearly ^^
Usually the listing will have additional info about what the fans are fans of, so please look through each site to get a better understanding of the content I enjoy!
I really enjoy 50x50 buttons can you tell :3c