First of all I searched on What a blog is before starting to use my blog. This is how I feel. The way I understood may not be the perfect.
A blog (shortened from weblog) is a web based method of collecting any information that you prefer. There is no restriction on what you can or can not blog, it is totally upto the owner to decide whether to have some informartion or not. This can be maintained as a diary, as a way of expressing your thoughts to the public, as a way of keeping track of the important information and also as a way of making a discussion with the viewers.
All the blogs are displyed with the timestamps and are sorted so that the new blogs are at the top. This makes easy for the visitors to view latest blogs. Blogs provide the visitors with the facility to submit comments, so that this can become a discussion.
A comprehensive description on "What a blog is":
en.wikipedia.org
www.answers.com
Create your own free blogs:
www.blogger.com
www.bloglines.com
Can you suggest some other sites that provide free blogs?