I'm sat here with Naomi, who's wondering what a Weblog is. 'Basically', I tell her, 'it's an online journal so that you can share your thoughts, links, pics etc. with anyone who's interested'.
For example, it could be used as a discussion site for people to get the latest information on products, support for software etc. Or it can be used collaboratively for work or school projects. Or it can just be so that you don't have to write mass-emails to let people know what you're up to while you're not in contact....