WordPress is a free and open source blogging tool and a content management system (CMS) based on PHP and MySQL which runs on a web hosting service. Features include a plug-in architecture and a template system. WordPress is used by over 18.9% of the top 10 million websites as of August 2013.WordPress is currently the most popular blogging system being used on the Web, powering over 60 million websites worldwide.
It was first released on May 27, 2003, by founders Matt Mullenweg and Mike Little as a fork of b2/cafelog. As of April 2013, version 3.5 had been downloaded over 18 million times.
One very popular feature of WordPress is its rich plugin architecture which allows users and developers to extend its abilities beyond the core installation. WordPress has a database of over 26,000 plugins each of which offers custom functions and features enabling users to tailor their sites to their specific needs. These customizations range from SEO (Search Engine Optimization) enhancers to content displaying features, such as the addition of widgets and navigation bars.
(Source: http://en.wikipedia.org/wiki/WordPress)
What You Can Use WordPress For?
WordPress started as just a blogging system, but has evolved to be used as full content management system and so much more through the thousands of plugins and widgets and themes, WordPress is limited only by your imagination. (And tech chops.)
(Source: http://wordpress.org/about)