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.
There is a large and vibrant community that supports and uses this system which means that many people are devoting countless hours to authoring improvements, developing dynamic plug-ins, and keeping the system stable and secure. The code is open, and much effort has been put into keeping it that way. This means that working on a WordPress platform insures that a site owner is never tied to a particular developer.
Being a fully developed database driven environment it has excellent provisions for aggregating content via categories and other taxonomy schemes. The core code is constructed to provide a firm baseline for any website application, and can be readily extended via plugins (free, premium & bespoke). The theming engine is quite mature and flexible which allows for an extensive array of customizations which can be executed in an impressive variety of ways.
CORE: There are no optional parts of the core code, all elements are active.
CONTENT STRUCTURE: Core code allows content to be freely associated via categories and tags, and theming structure provides for manipulation of layout and visibility of content. Unique content types can be created via theme coding.
USER EASE: The administrative interface is straight forward and has a shallow learning curve
ADAPTABILITY: Core functions can be readily extended via community sanctioned plugins, and the theming structure allows for conditionally applied template files
Of the three most popular open source content management systems WordPress holds the number one position in terms of reach and popularity. As of early 2013 it is estimated that over 17% of all currently active websites are built on the WordPress platform.
The reasons for this prevalence are many, but high on the list is the fact that the administration interface is very streamlined and easy to grasp for a standard site owner. However, this spareness of visible administration functions can be misleading as much can be accomplished to extend the way a WordPress site looks and behaves via custom programming in the theme.