A blog is like an online journal. Entries are arranged chronologically with the newest entries listed first.
The blog and the wiki share the same simple editing toolbar and thus share a lot of the same advantages. The biggest difference between a blog and a wiki is that the blog has a sense of time, but the wiki doesn't. In a blog, new content is found more easily than older content. In a wiki, content is found by need or by navigation, rather than by time.
Blogs are available for users and groups. Users can edit their own blog as well as group blogs they have access to.