Read: What is a Blog?

What do you think is a Blog?
A blog (also called a weblog or web log) is a website consisting of entries (also called posts) appearing in reverse chronological order with the most recent entry appearing first (similar in format to a daily journal). Blogs typically include features such as comments and links to increase user interactivity. Blogs are created using specific publishing software.

Variations of the term blog:
    Blogging: The act of writing a post for a blog
    Blogger: A person who writes content for a blog
    Blogosphere: The online community of blogs and bloggers

The Birth of Blogs:
The earliest blogs started in the late 1990s as online diaries. Individuals posted information on a daily basis about their lives and opinions. The daily posts were listed in reverse date order, so readers viewed the most recent post first and scrolled through previous posts. The format provided an ongoing inner monologue from the writer. As blogs evolved, interactive features were added to create a two-way conversation. Readers took advantage of features that allowed them to leave comments on blog posts or link to posts on other blogs and websites to further the dialogue.

 Blogs Today:
As the Internet has become more social, blogs have gained in popularity. Today, there are over 100 million blogs with more entering the blogosphere everyday. Blogs have become more than online diaries. In fact, blogging has become an important part of the online and offline worlds with popular bloggers impacting the worlds of politics, business and society with their words.

Research: http://weblogs.about.com/od/startingablog/p/WhatIsABlog.htm