What is a blog?

Blog - Wikipedia:

A blog (a portmanteau of "web log") is a website where entries are written in chronological order and displayed in reverse chronological order. "Blog" can also be used as a verb, meaning to maintain or add content to a blog.

Boing Boing: Blog defined:

Blog noun [short for Weblog] (1999) : a Web site that contains an online personal journal with reflections, comments, and often hyperlinks provided by the writer.