Multi-author posts are exactly as they sound. They're posts that multiple people have edit rights to! This is mostly meant for big group posts where the group is either a bunch of admins, guild leaders, etc. All edits are recorded just as normal, and it's like a giant group post.
For specifics, the post still has an owner, the person who first wrote it. They start it, then add in their cohorts and blamo! If someone happens to add something rule breaking to the thread, we will know who did it and there won't be any sort of wrongful punishment.