In computing, a content management system (CMS) is a document centric collaborative application for managing documents and other content. A CMS is often a web application and often it is used as a method of managing web sites and web content. The market for content management systems remains fragmented, with many open source and proprietary solutions available.
See the Wikipedia entry here
The JBoss Content Management System (CMS) is implemented using a WebDAV interface into a Subversion repository. The CMS does not implement several aspects of full blown CMS systems such as Workflow, Indexing and Searching, or Templating, as some CMS systems do, but it is simply a way of storing your content in the and making it available to the rest of the world.
There is nothing stopping anyone from using a larger CMS system on top of the CMS since it is fully available via WebDAV. May open source and commercial CMS systems have the ability to manage content in WebDAV repositories.