Generally a writer who posts his work regularly on a website is called a blogger.
The act of writing a blog is called blogging. Blogging has now become a profession. Many people are full time bloggers and enjoy making money online through affiliates and advertisements.
A blogger generally has skills in writing quality content and strong passion towards their niche. They may also have knowledge about HTML, CSS, XML, SEO etc.(not required though).
Blogger should not be confused with blogger.com. blogger.com is a blog publishing service which is provided for free by Google.