CMS is a software application that allows users to create and manage website content without needing HTML knowledge. It provides features like selective access permissions for security, flexibility for non-technical users to publish content easily, and collaboration tools to allow teams to work on content simultaneously. CMS makes it possible to update websites independently, access the latest functionality without a full site overhaul, and manage an entire internet marketing strategy from one place. Reasons to use a CMS include having SEO-friendly URLs, multi-lingual support, and enabling quick and easy page management.