what is it?

What distinguishes a blog/vlog from any other website? So someone very dear to me who is a videoblogger told me that one major thing is that the blog/vlog allows, invites, encourages viewer to comment. It encourages interaction between the creator and the viewer. Is that the defining point? Are there other things that makes blog/vlog distinct? Another thing he pointed out was that the format of a blog/vlog makes it easy for changes/updates to be made. Content additions push old content down the page. Easy of content modification, a format for content management, doesn't seem to be a satisfactory definition for what makes blog/vlogs distinct. There seems to be something about the fact that the visitors and the creators can interact.