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 more than 18.9% 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.
WordPress users may install and switch between themes. Themes allow users to change the look and functionality of a WordPress website or installation without altering the information content or structure of the site. Themes may be installed using the WordPress “Appearance” administration tool or theme folders may be uploaded via FTP. The PHP, HTML & CSS code found in themes can be added or edited for providing advanced features. Thousands of WordPress themes exist, some free, and some premium (paid for) templates.
One very popular feature of WordPress is its 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.
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 WPMU) was a fork of WordPress created to allow multiple blogs to exist within one installation but is able to be administered by a centralized maintainer. WordPress MU makes it possible for those with websites to host their own blogging communities, as well as control and moderate all the blogs from a single dashboard. WordPress MU adds eight new data tables for each blog.
As of the release of WordPress 3.0, WordPress MU has merged with WordPress.