A blog is a personal diary. A daily pulpit. A collaborative space. A political soapbox. A breaking-news outlet. A collection of links. Your own private thoughts. Memos to the world.
Your blog is whatever you want it to be. They come in all shapes and sizes, and there are no real rules.
In simple terms, a blog is a web site, where you write stuff on an ongoing basis. A blog is a web page that contains brief, discrete bits of information called posts. These posts are arranged in reverse-chronological order (the most recent posts come first), so your visitors can read what's new. Then they comment on it or link to it or email you. Or not.
Some additional information on blogs can be found here.
