WordPress is an open source web authoring system that allows site owners to edit and control the content of their site via a browser based admin interface.
Content is stored in a MySQL database, and PHP code is used to extract that content and translate it into presentable and standards compliant HTML.
WordPress is by far the most popular web authoring system world wide for a variety of reasons including:

• Prevalence of WordPress as a CMS.
• Commitment of project to backwards compatibility and a continuous line of development.
• Ease of use for non-technical editors.
• Compatibility with social media and SEO best practices.