A content management system (CMS) is a computer application that allows publishing, editing, and modifying content on a website. It offers advantages like being easy for developers to use, cost effective, flexible, and able to be maintained over time. Popular CMS platforms include WordPress, Drupal, Joomla, Textpattern, SilverStripe, and MODX. Examples of websites that use CMS include icondock.com and social.ford.com.