What is a Blog?

I am about to teach a course on “The Essay” and that leads me to ask what is a blog? I know that blogging platforms, like WordPress, can be used to share fiction, poetry, technical manuals, and more, but in its general form of personal reflections what is a blog?

It’s a journal or diary, I expect some to answer. Yet is a diary normally so public a document?

Could we consider blogs essays? I believe there’s a case to be made for categorizing most blogs as creative non-fiction, and as essays in particular. I’m going to be reflecting on this question over the weekend. I hope to offer a better answer in a few days.