WordPress is a free and open source content management system that allows users to build websites and blogs. It can be self-hosted (WordPress.org) for full control over themes, plugins, and functionality or used through WordPress.com for a simpler hosted option with limited customization. Key aspects of WordPress include using pages for static content, posts for time-based blog content, categories and tags to organize content, plugins to extend functionality, and widgets to customize the site interface. Setting up and maintaining a WordPress site requires attention to security, themes, plugins, SEO, analytics and social media integration.