A Content Management System (CMS) allows publishing, editing, and modifying content on a website from a central interface. It provides basic functionality like lifecycle management of content, templates, and a central repository. Popular CMSs include WordPress, Drupal, and SharePoint. WordPress is a free and open source CMS that is easy to use and has thousands of free themes and plugins available. It allows users to create and manage blog content or websites through a web-based user interface.