A blog is a regularly updated website that is typically ran by either one indicidual or a small group of individuals. A blog is often written in a conversation sort of style. Blogs can bring the news to people or they can just be a funway to share your thoughts with others over the web.
Blogs can be like personal diaries or they can be a bit more formal than a diary. Blogs have become really popular ways to connect to other people, sometimes in a meaningful way.