The word of the year is "blog."

So says Merriam-Webster, and it should know. The dictionary giant named "blog" as the most popular word of 2004, based on how many visitors to its Web site asked for a definition.

It isn't surprising: Blogs have been in the news a lot, and for the first time blog writers were given press credentials for both the Democratic and Republican conventions.

For the uninitiated: Think of a blog - it's short for Web log - as a cross between an online diary and a news ticker. Blog owners update them regularly with all sorts of information and commentary.

Josh Humphries, a writer and political consultant in Roanoke, has three.

One he posts to infrequently, "to bounce ideas off other people." Another is just for "personal stuff and for ... passing along stupid little [bits of knowledge]." His third focuses on "'subkultures,' where I bounce ideas about music and culture off other people."

Blogs are becoming a powerful medium for information to spread, as more people turn to the Internet for their news.

In his book "We the Media," San Jose Mercury News columnist Dan Gillmor writes that blogs are "one of the healthiest media developments in a long time. We are hearing new voices ... Blogs can be acts of civic engagement."

There are many kinds of blogs, just as there are many kinds of books - short and long, with pictures and without, professional and amateur. What they have in common is that new entries are added regularly while old ones can still be read.

And an "entry" can be anything. Some bloggers keep them short - humor columnist Dave Barry's (weblog.herald.com/column/davebarry) are usually no more than a short quip and a link to something funny.

Other bloggers post a few sentences every day (or week, or hour) describing their day or commenting on something they read or saw. Some people post bad poetry or talk about their family. Some maintain "photo blogs," often using pictures taken with camera phones.

Still others - and these are the ones that typically make the news - write a lot more. Entries are frequent and can be several paragraphs long, including references, links and lots of information. Politics is a hot topic, with sites such as Talking Points Memo (www.talkingpointsmemo.com) and Instapundit (www.instapundit.com) offering perspective from the left and the right, respectively.

Some are good, some are bad. Some are thought-out, crafted works; others are barely readable diatribes. And many allow readers to comment, extending the conversation.

There are blogs out there on every subject, from every point of view. Technorati, a site that tracks blogs, is watching almost five million of them. There's a blog for every interest.

"My audience differs from blog to blog," Humphries said. Some are interested in the technical ("I talk about my theories about phenethylamine precursors occurring in nature"), others are for friends, and some posts are for anyone who's interested in the details of his life. "I do get personal, and people tend to react in a positive way to it," he said. "They tend to tell me that they appreciate my candor."

Personal blogs are often full of that candor, and sometimes that means trouble for the writer. Delta Airlines recently fired one of its flight attendants whose "Queen of Sky" blog (queenofsky.journalspace.com) featured photos of her in suggestive poses. Microsoft fired an employee who posted a photo of Macintosh computers being delivered to the company.

When your diary is an open book, not everyone will like what they read, and few bloggers have the legal resources that the mainstream media have. Sony sent its legal team after blogger Jason Kottke (www.kottke.org), after he posted a transcript of "Jeopardy" champ Ken Jennings' game-losing episode, even though The Washington Post printed the same information. Kottke took the entry down.

On the other hand, many companies are taking advantage of blogs. They see them as a way to give the world insight into what they're doing - but with a lot less formality than a press release. Technology companies often let their developers post comments about ongoing projects, the thinking that went into a piece of software, or even what's being served in the company cafeteria.

And it's not just the employees; upper management is getting into the act. Pat Matthews, chief executive officer of Excedent Technologies in Blacksburg, is author of the "Small Town, Big Ideas" blog (patmatthews.typepad.com). Matthews says he started blogging for several reasons.

"I believe it is important that I communicate my thoughts and ideas to those around me," he said, "A blog is a great way to do this."

Matthews uses his blog as a tool, not just a place to vent.

"We've been raising capital lately and I've sent my blog out to potential investors," he said. "Perhaps more than anything, my blog helps me to build credibility as the CEO of a young company."

Whether personal or professional, long or short, what gives blogs their real power is that they link to one another. Some popular blogs consist of little more than links.

A group of linked blogs can spread information like wildfire, and together they form what's been tagged the "blogosphere." An interesting story can make it from coast to coast in a heartbeat.

According to Technorati, for example, more than 9,000 blogs link to BoingBoing, one of the most popular blogs on the Internet. And BoingBoing itself links to thousands of others. That makes blogs the water cooler of the online world. If you want to know "What are people on the Net saying about such-and-such," you'll find an answer on blogs.

The stories that circulate fastest in the blogosphere are the ones that people find most interesting. They might be as big as a political scandal, such as when former Senate majority leader Trent Lott was forced to resign that post. A racist comment of his had been circulating on blogs.

Or they might be just a provocative photo: When The Roanoke Times ran a shot of a local woman smoking while complaining about jackhammers' noise harming her fetus, it didn't take long for bloggers to notice, and for the photo to begin popping up all over.