What is blog?
http://en.wikipedia.org/wiki/Blog

A BLOG refers to a private webpage which is published by either an individual or a group of individuals.

BLOGS are commonly personal journals/diaries and are used to comment on all sorts of topics depending on the interests of the blogger (author).

A BLOG is usually updated frequently, maybe monthly, weekly or even daily, it all depends on the blogger.

Most blogs enable the visitors to post comments and/or suggestions allowing interactivity between the blogger and the visitors.

Blogging

This describes the actual act of creating or updating a blog.

It is fairly easy to set up your own BLOG on the subject of your choice.
Now you know what is blog.