A content management system (CMS) is the collection of procedures used to manage work flow in a collaborative environment. These procedures can be manual or computer-based. The procedures are designed to do the following:
In a CMS, data can be defined as nearly anything: documents, movies, pictures, phone numbers, scientific data, and so forth.
A web content management system is a CMS designed to simplify the publication of web content to web sites and mobile devices — in particular, allowing content creators to submit content without requiring technical knowledge of HTML or the uploading of files.
Several web-based content management systems exist both in the Open Source and commercial domains.
In my opinion, the Joomla CMS is one of the best available.