A content management system (CMS) is a computer application used to manage work flow needed to collaboratively create, edit, review, index, search, publish and archive various kinds of digital media and electronic text.
Among the many Content Management Systems (CMS) out there right now, doing a simple search on Google for "Content Management Systems" or plainly "CMS" will yield anywhere from 143,000,000 to 248,000,000 potential results.

A content management system (CMS) such as a document management system (DMS) is a computer application used to manage work flow needed to collaboratively create, edit, review, index, search, publish and archive various kinds of digital media and electronic text.
CMS' are frequently used for storing, controlling, versioning, and publishing industry-specific documentation such as news articles, operators' manuals, technical manuals, sales guides, and marketing brochures. The content managed may include computer files, image media, audio files, video files, electronic documents, and Web content. These concepts represent integrated and interdependent layers. There are various nomenclatures known in this area: Web Content Management, Digital Asset Management, Digital Records Management, Electronic Content Management and so on. The bottom line for these systems is managing content and publishing, with a workflow if required.
A CMS may support the following features:
Source: Wikipedia