1. What is a CMS ?

A content management system (CMS) is a 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:

• Allow for a large number of people to contribute to and share stored data
• Control access to data, based on user roles. User roles define what information each user can view or edit
• Aid in easy storage and retrieval of data
• Reduce repetitive duplicate input
• Improve the ease of report writing
• Improve communication between users

In a CMS, data can be defined as almost anything - documents, movies, pictures, phone numbers, scientific data, etc. CMSs are frequently used for storing, controlling, revising, semantically enriching, and publishing documentation. Content that is controlled is industry-specific. For example, entertainment content differs from the design documents for a fighter jet. There are various terms for systems (related processes) that do this. Examples are web content management, digital asset management, digital records management and electronic content management. Synchronization of intermediate steps, and collation into a final product are common goals of each.

Video Answer
http://drupal-videos.blogspot.com/2014/06/1-what-is-cms.html