WordPress is a free and open source blogging tool and a content management system (CMS) based on PHP and MySQL. Features include a plugin architecture and a template system. WordPress was used by more than 22.0% of the top 10 million websites as of August 2013. WordPress is the most popular blogging system in use on the Web, at more than 60 million websites.

It was first released on May 27, 2003, by its founders, Matt Mullenweg and Mike Little, as a fork of b2/cafelog. The license under which WordPress software is released is the GPLv2 (or later) from the Free Software Foundation.

WordPress first appeared in 2003 as a joint effort between Matt Mullenweg and Mike Little to create a fork of b2. Christine Selleck Tremoulet, a friend of Mullenweg, suggested the name WordPress.

In 2004 the licensing terms for the competing Movable Type package were changed by Six Apart and many of its most influential users migrated to WordPress. By October 2009 the 2009 Open Source content management system Market Share Report reached the conclusion that WordPress enjoyed the greatest brand strength of any open-source content-management systems.