More and more, people don't have traditional websites: static things where pages can be added, updated or taken away. Instead, they write new material for their website when they feel like it, and then put it up on one page, with the most recent writing first. These people are running weblogs.
How Did Weblogs Start?
Many people say that there have been weblogs (or blogs, as they're sometimes called) for as long as there has been a web. Back when there were only a few thousand websites, the 'What's New' page that announced each new one (yes, there really was such a thing!) worked in just the same way as blogs do today.
Early weblogs included Scripting News, Robot Wisdom and Camworld, which all started in 1997. To begin with, blogs mostly consisted of often-updated lists of useful and amusing links to other websites, but it gradually became clear that the format was just as good for distributing longer articles. Blog software started to be developed, and their popularity quickly exploded. By 1999, everyone was talking about blogs.
Why are Blogs So Popular?
In recent years, the blog format has very much taken over from the 'personal home page'. People seem to find it much easier to just put a kind of public diary online, instead of putting up a little biography of themselves and a collection of articles. It's more personal, more fun, and more interactive day-to-day.
Businesses have started to open blogs too - in many ways, they're like a replacement for newsletters. A regularly-updated blog gives customers a great sense of what a business is like, while giving the business a great way to keep communicating with its customers and being useful to them, even when they're not buying anything right this minute.
In my opinion, the biggest reason for blogs' popularity is that they make publishing to the web very easy. You don't really have to know anything about what's happening behind the scenes: blogs finally make publishing your thoughts for everyone to see as easy as posting to a forum or sending an email. In a way, blogs fulfil the original promise of the web.
Today, there's a lot of blog software out there - if you want a blog, you're spoiled for choice. What you get will depend on how comfortable you are with technical stuff, and whether you want it to be part of your main website or not.
Movable Type. This is software that you install on your web server. You simply log in and type your post, and it creates your pages for you. Movable Type can be a little complex to set up, but you can use a version called Typepad that is hosted by its creators instead of using your server.
Blogger. You don't install Blogger on your server - instead, you give it your FTP password and let it upload files to your web server for you. If you don't have any hosting, you can also host blogs for free at Blogger's Blogspot. Blogger is owned by Google.
WordPress. WordPress is a free alternative to blogging software. It works in basically the same way as Movable Type, but without the restrictive licensing and with nicer-looking default templates. Many people have switched to WordPress out of frustration with Movable Type and not looked back. You have to host it on your own server, but it's very simple to set up - don't be scared!
LiveJournal. LiveJournal is a completely online service, meaning that it has nothing to do with your website, except that you can link to your LiveJournal if you want. LiveJournal is more social than most blogging, allowing you to join communities relating to your interest.
There are plenty of other online services, but they're all pretty much the same: MSN Spaces, AOL Journals, and so on. You're unlikely to get taken very seriously if you have a blog at any of these places, although it'd be easy. In the end, it's all about power versus convenience: the more work you put in to get your blog working, the more likely that it's going to be what you really wanted it to be. If you're creating a website anyway, you'd be silly not to put a blog on it.