A blog is a type of website that is usually arranged in chronological order from the most recent ‘post’ (or entry) at the top of the main page to the older entries towards the bottom. ~Darren Rowse
Well that is a “traditional” and “literal” definition of blogging, isn’t it? My first impression of blog was a web-space where people wrote on various topics and everyone had their own web space to do it. So I guess this definition is better :-
A blog is merely a tool that lets you do anything from change the world to share your shopping list.