What is a blog you may say? A blog is like a journal online, only it has the capacity to be much more powerful. It is a website that is ordered chronologically with newer posts (paragraphs or messages) at the top of the page and older posts below.
In my opinion, the most powerful part of a blog is the ability to let others comment on your posts. Some blogs do not allow this feature but the vast majority do. These comments may be used for feedback, questioning, or just plain commenting about the post.
Blogs allow for great discussion on many different topics and through various means. Blogs can virtually be worked on at any time as long a "blogger" has internet connection and a computer.
Blogs can be used in school for collaboration, discussion, or even scaffolding students.