A CMS or Content Management System is a software with which content is managed. In most cases, this refers to the maintenance of content on websites. A user-friendly interface allows users without programming skills to create and update text and media content.
We at von Rabenstein prefer to use the CMS "Contao" for our websites - as we have had the best experience with regards to usability for non-professionals over the years. Furthermore, the technical basis is rock solid, very adaptable and expandable. Another possibility is always Wordpress - here the distribution is unbeatable.