What is "cms"
CMS stands for Content Management System, or in good English, Content Management System.
Essentially, a CMS aims to facilitate the creation, editing, publication and distribution of information. Imagine a CMS as a skeleton of a web site, only needing you to fill this skeleton with content, which is the information you want to share.
A CMS has several advantages for two main types of audience. To start a CMS is excellent for someone who wants to have a web site but has no technical knowledge, time or money to produce a site or hire third parties to do so. With a CMS, the technical knowledge to put it to work is very small (but not non-existent), and the editor only needs to worry about developing (or paying to develop) a layout of his own. But if he doesn’t care about it, he can use ready-made themes distributed for free.
On the other hand, CMS also facilitates the lives of developers, as they present several ready-made solutions (example: poll, comment system, user management, forum, contact form, among other things), reducing development time, and allowing developers to focus on producing more specific solutions and producing layout.
Where I work, we use our own CMS, created internally. The system does not have as many modules as Drupal, for example (because its creation is very recent), but the goal is the same (for us developers): reuse of code, reducing development time.
There are Open Source and Closed Source content managers, as well as free and of course paid content managers. In addition, there are CMS for every type of site and taste: there are the specific ones, such as Wordpress (for blogs) and Bbforum (for forums), and there are also generic or large content portals, such as Drupal or Mambo itself.