What is a "blog"?
"Blog" is an abbreviated version of "weblog," which is a term used to describe web sites that maintain an ongoing chronicle of information. A blog is a frequently updated, personal website featuring diary-type commentary and links to articles on other Web sites. Blogs range from the personal to the political, and can focus on one narrow subject or a whole range of subjects.

Many blogs focus on a particular topic, such as web design, home staging, sports, or mobile technology. Some are more eclectic, presenting links to all types of other sites. And others are more like personal journals, presenting the author's daily life and thoughts.

Generally speaking (although there are exceptions), blogs tend to have a few things in common:

A main content area with articles listed chronologically, newest on top. Often, the articles are organized into categories.
An archive of older articles.
A way for people to leave comments about the articles.
A list of links to other related sites, sometimes called a "blogroll".
One or more "feeds" like RSS, Atom or RDF files.
Some blogs may have additional features beyond these.