CMS stands for “Content Management System”, also called “backend” or “administration” interface. Basically, it’s a password-protected website allowing you to update yourself the content of your “frontend” (publicly visible) website.
Many opensource or commercial packages exist that can reduce project costs but in many cases, it is worth investing in a tailor-made CMS that is closely tied to your business ‘s specific processes and needs, resulting in a less cluttered, more user-friendly working environment.
Personally, i either use Wordpress, Drupal or custom-made ones.