CMS means Content Management System
A content management system (CMS) is a computer application that supports the creation and modification of digital content
It is often used to support multiple users working in a collaborative environment.
CMS features vary widely. Most CMSs include Web-based publishing, format management, history editing and version control, indexing, search, and retrieval. By their nature, content management systems support the separation of content and presentation.
A web content management system (WCM or WCMS) is a CMS designed to support the management of the content of Web pages. Most popular CMSs are also WCMSs. Web content includes text and embedded graphics, photos, video, audio, maps, and code (e.g., for applications) that displays content or interacts with the user. A well known and often used CMS is WordPress
Source: Wikipedia