Wikipedia helpfully informs me:
"A blog (a portmanteau of web log) is a website where entries are written in chronological order and commonly displayed in reverse chronological order. "Blog" can also be used as a verb, meaning to maintain or add content to a blog.
Blogs provide commentary or news on a particular subject such as food, politics, or local news; some function as more personal online diaries. A typical blog combines text, images, and links to other blogs, web pages, and other media related to its topic. The ability for readers to leave comments in an interactive format is an important part of many blogs. Most blogs are primarily textual, although some focus on art (artlog), photographs (photoblog), sketchblog, videos (vlog), music (MP3 blog), audio (podcasting) or sexual topics (Adult blog), and are part of a wider network of social media.
In May 2007, blog search engine Technorati was tracking more than 71 million blogs."
Now I am part of it: this was my first blog.