The opposite of a troll in an online community. While a troll looks for attention and chaos, gnomes work quietly in the background fixing things. They usually frequent forums or wikis, organizing information and fixing errors.
1. I changed Sarah Jessica Parker's picture on wikipedia to a horse, but some gnome fixed it before I could show anyone.
2. I never know where to post new topics, I just stick them somewhere random and the gnomes come and put them where they belong.