WordPress is a free and open source blogging tool and a content management system (CMS) based on PHP and MySQL. It has many features including a plug-in architecture and a template system. WordPress is used by over 16.7% of Alexa Internet's "top 1 million" websites and as of August 2011 manages 22% of all new websites. WordPress is currently the most popular blogging system in use on the Web.

It was first released on May 27, 2003, by founders Matt Mullenweg and Mike Little as a fork of b2/cafelog. As of December 2011, version 3.0 had been downloaded over 65 million times.

Plugins

One very popular feature of WordPress is its rich plugin architecture which allows users and developers to extend its abilities beyond the features that are part of the base install; WordPress has a database of over 22,000 plugins with purposes ranging from SEO to adding widgets.

Widgets

Widgets are small modules that offer users drag-and-drop sidebar content placement and implementation of many plugins' extended abilities. Widgets allow WordPress developers to add functionality to their sites. These small modules can be used to add functionality such as a slideshow, Facebook Like box, small news slider, and more

Multi-user and multi-blogging

Prior to WordPress 3.0, WordPress supported one blog per installation, although multiple concurrent copies may be run from different directories if configured to use separate database tables. WordPress Multi-User (WordPress MU, or just WPMU) was a fork of WordPress created to allow multiple blogs to exist within one installation that is able to be administered by a centralized maintainer. WordPress MU makes it possible for those with a website to host their own blogging community, as well as control and moderate all the blogs from a single dashboard. WordPress MU adds eight new data tables for each blog. WordPress MU merged with WordPress as part of the 3.0 release.