WordPress is a content management system that allows non-technical users to easily create and manage websites through a user-friendly interface. It provides features like a WYSIWYG editor, presentation layers, and the ability to enhance functionality through plugins. The document discusses modifying WordPress themes to change appearance while preserving core functionality. It also covers how to work with the PHP and CSS files that control what elements are displayed and how they are styled on the site. Plugins and widgets are mentioned as ways to extend WordPress functionality and add dynamic elements to sidebars.