A content management system (CMS) allows users with little knowledge of web development to create and manage a site's content. Instead of calling on a web designer to make changes, staff can do it for themselves.
Creating a site using a CMS requires more development time initially, but once in place means staff can manage it for themselves. Pages can be edited, created or moved, images and video uploaded, and more, all using a browser based interface aimed at non-technical users.
If your site has requirements that can't be met by existing systems we can discuss options for a bespoke CMS. Otherwise, I would recommend using an existing system such as WordPress, with a customised theme to match your branding and design guidelines.