What's a blog?

[joanna bujes]

OK. I understand it's short for "web log," but what's a web log? It sounds 
like something a browser might maintain privately, like a log of all the 
links you go to...

...but obviously that's not what it means because people use it more in the 
sense of "web page."

So, please, what's a blog?

Thanks,

Joanna