A blog is an authoritative voice in the community. A blogger (or team of bloggers) distributes information in a blog post to an audience who's involved with the post subject matter. Blogs are best suited to providing announcements, news, experience accounts or expert opinions on the subject of the blog. They and their data are tied to a group where the blog is located.
Not all groups that you belong to (or have permission to view) will have a blog, but lots do.
(The following capture shows a coaching matchday experience blog post.)