Livejournal is a website that hosts blogs. Individuals may sign up free for a Livejournal (LJ for short), list other LJ users as friends, view a page called a "Friends List" that produces the blog entries of people you friend, in chronological order. As well as LJs for individuals, there are LJ Communities.
A lot of fandoms are exist on LJ due to the ease of information distrubution, and the comfort in blending personal and public spaces.
LJ is the largest single site of creative fanworks.
Similar journalling sites - eg InsaneJounral, JournalFen, Dreamwidth and Greatest Journal - have a small representation of the fandom.