I still hear this question frequently - and I'm not alone.
Blog is short from web log, an online diary or newsletter made up of a
series of posts or stories. You're reading a blog post right now.
The Wall Street Journal did a story last week about business blogs,
titled, "What the In-Crowd Knows."

People who follow electronics got an early peek at a key new product when Engadget posted photos of Microsoft Corp.'s
XBox 360 videogame console a week ahead of its debut. TV executives
keep tabs on which networks are ordering and canceling shows. Doctors
and others in health care can link to the latest news and commentary on
drug marketing. Reporters and media watchers turn to Jim Romenesko, who
runs a blog on the Poynter Institute's Web site.

There are three basic varieties of blogs: those that post links to
other sources, those that compile news and articles, and those that
provide a forum for opinions and commentary. Some do one of these
things or mix all three.

The story goes on to mention a couple of health care blogs, along with
examples of blogs from other industries. You can check out some of my
favorite health care blogs in the Blogroll located in the nav bar
on the right side of the screen. On my list, and noted in the WSJ, is
Matthew Holt's The Health Care Blog. There is also a weekly round up of
health care blogging, check out Grand Rounds - this weeks host is code blog: tales of a nurse.