A CMS or Content Management System involves both content and structure and the tools required for handling content and structure.

Ok let's take an example. The most common usage of a CMS is to build and just as importantly, maintain a website.  The old way of website buiding was pretty much an ad hoc process and what you end with can be a management headache particularly for those with limited technical expertise.

Using A CMS provides a structure to your site that you can use to deploy information and editing tools for modifying or updating content as required. Additionally, since the CMS takes a structured approach your website maintenance is far simpler and faster!  The site you are looking at was built with CMS! It looks good and is easy to maintain!