I have only started blogging recently, even though I have been building web sites for nearly twelve years.
What I find interesting about blogs is how people define them.
I have tried to define blogs in two distinctive ways :
A (1 to 13) : from a functional and technical perspective
B (1 to 7) : from a conceptual and more emotional perspective
Main characteristics :
A1 Title, each article/post/note has a title
A2 Date (optionally time), each article/post/note has an indication of when it was created.
A3 Content/Body, each article/post/note has content that is the main body, however it is possible that title and content be the same length in certain cases.
A4 Comments, each article/post/note allows users to post comments. Some systems have central user authentication systems that will recognize users and authenticate them so they can post as a recognized user.
A5 Permalink, each article/post/note has a specific URL/address that will display the article/post/note in full and generally followed by the comments
Common Options :
A5 Author, articles/posts/notes will have an indication of the name of the author or a nickname/handle of the author
A7 Categories/Tags, when each article/post/note is created, the creator usually can indicate which categories/tags it is associated with.
A8 Trackback, blogs are precursors in this area, the trackback is basically an automated communication system that will inform another blog/system that a message has been posted about an article/post/note. When an article/post/note is written on blog A about something on blog B, blog A automatically pings blog B to inform it.
A9 Archives, blogs usually have links to archives and or previous articles/posts/notes sorted by months
A10 Order, blog comments are usually displayed after the article/post/note, in reverse chronological order (the most recent is displayed first)
Back-end Functions :
A11 Users or groups of users will be authenticated and thus gain access to a type of dashboard that will allow them to create and often preview before publishing the article/post/note.
A12 Categories/Tags and Pages and of course the articles/posts/notes can be managed using a WYSIWIG or form based system like the articles/posts/notes
A13 Themes and Plugins, Blog systems allow bloggers to heavily customize/personalize the look and feel of their blogs as well as adding specific functions like contact pages, photo galleries etc.
Conceptual and Emotional Perspectives :
B1 Opinions, blogs are often defined as being personal accounts/diaries/journals
B2 Theme, blogs and the content often have a central underlying theme
B3 Types, blogs are often professional or personal and sometimes group based
B4 Discussion, blogging is closely associated with the idea of discussion via the concept of posting comments about the article/post/note
B5 Personal, blogs often present themselves as the work of a person or a group of people and do so with an about page and more often than not with a photo. This instantly gives personality and creates a link/bond with the writer that is often lacking in many online newspapers/magazines.
B6 Free, on a par with the founding spirit of the Internet, blogs are so far, in the vast majority, free to create and use. This is one of the nice sides of blogging in that it resembles a large freedom of speech movement. Specific and extra user needs like having your own domain name are obviously available at a price...
B7 Easy to use, blogs do not really require knowledge of any programming language and each new version of the most well known systems makes things easier and bring new interesting functions to the blogging world. A lot of networking functions like trackback to inform others of what you have posted are automatically handled without any user intervention required.
What Blogs are not :
Forums are not usually like blogs. In a forum multiple users can post articles/content and multiple users can post comments. When following a thread of posts in a forum it is often difficult to differentiate between the first post and the following posts. It would be possible to set-up a forum whereby the initial message in a thread could only be posted by a specific user or group of users and only then could others respond, however this is not how forums are traditionally set-up. Unlike blogs where discussions evolve from one point, forums allow multiple starting points for discussion. Blogs also seem to link more between each other and between posts/notes than forums do.
Newsgroups are pretty different to blogs. Newsgroups are not only different in form but also technically in the way they work. Groups on newsgroups are replicated over multiple servers all over the world which rarely happens with blogs in fact I don't know of an example. Newsgroups are just messages posted to a specific group and depending on the software used to read the messages links and/or associations between messages can be hard to figure out unlike in forums. There is no real structure in commenting on an initial post in newsgroups since links between posts are not that easy to establish. Newsgroups are also well known for multi-part binary posts of images, video and all sorts of other file formats on top of text messages.
CMS, I've worked on creating web sites using Content Management Systems (CMS) like Vignette StoryServer and recently Gossamer Threads Links (can be considered a CMS). With this experience in mind I tend to disagree with most blog fanatics in their will to differentiate themselves with CMS systems. There is no real need to debate here, professional CMS software is capable, when properly configured, to provide everything blogs provide, and more (hence the extra cost involved).
Most CMS can be set-up to look and work exactly like blogs. From this point onwards blog fanatics tend to turn to the quoted conceptual and more emotional definition of a blog to argue differences between a CMS and blogs which can obviously also be replicated...
Blog Trivia :
One of the first bloggers Justin Hall started with a site called links.net
Web log was first used in 1997 by Jorn Barger and was first shortened to blog in 1999 by Peter Merholz
Open Diary first started the article with comments system in 1998