A blog -- short for "web log" -- is an online personal journal that covers topics ranging from daily life to technology to culture to the arts. Blogs have made such an impact this year that Merriam-Webster named it the word of the year.
"There's a blog for every niche. There's a blog for every interest," said technology writer Xeni Jardin, who co-edits the blog boingboing.net.
Dylan Verdi, an 11-year-old known as the world's youngest videoblogger, says she covers "things that I've seen that I like or that I've heard of, or just anything that happened to me that day that I'm thinking."
There are millions of blogs on the Internet -- a new one is created every seven-and-a-half seconds. More than 10,000 new additions are added to the "blogosphere" each day.
This week, their influence has become readily apparent. Dozens of bloggers have been filing firsthand reports from the areas devastated by southern Asia's deadly tsunamis.
"There is kind of an immediacy that people can relate to -- can't help but relate to that in a very intimate way," said Jardin.
"Day three," one blogger writes from the scene, "this may be an unexpected challenge and responsibility, and it hurts to see people in pain. But it's also a remarkable experience to be on hand to do something modest, but useful, in the aftermath of a disaster."
Bloggers around the world have made themselves useful, encouraging donations to relief groups, posting the names of the missing and expressing sympathy for the victims.
As a driving force in politics this year, bloggers covered the 2004 presidential campaigns and election. Political candidates also used them as valuable campaign tools.
"The Internet taught us, rather than the other way around," said former Democratic presidential candidate Howard Dean.
This year, for the first time, bloggers were permitted to cover the national political conventions firsthand.
Bloggers have taken the lead over traditional media on a number of stories, including racist remarks made by then-Senate Majority Leader Trent Lott, R-Miss., at former Sen. Strom Thurmond's birthday party.
"Suddenly the mainstream media, the nightly news, on all three networks and on cable, picked up the story and the papers picked up the story and the next thing you know, Trent Lott's resigning and gone," said Democratic strategist Joe Trippi, who masterminded Dean's groundbreaking online campaign efforts.
Some of the most compelling images of 2004 found their way to blogs first, from the Florida hurricanes to the war in Iraq. It was a blogger who got the first photographs of coffins carrying U.S. soldiers arriving in the United States from Iraq.
But for Verdi, it is the simple pleasure of knowing that someone is listening that makes blogging worthwhile.
"On my blog it allows people to post comments, and I have gotten comment upon comment upon comment," she said. "It makes me feel really good that somebody else cares about what I have to say."
ABC News' Elizabeth Vargas filed this report for "World News Tonight."